Problem with trying to erase hard disk

Try the following:

-Reset SMC - http://support.apple.com/kb/HT3964

-Insert install dvd

-shut down mac

-Boot mac while holding the ALT key, this option should show you within the minute (give it 2) an icon of the inernal HD & the install DVD.

-If so, select the install DVD - give it some time to boot from the DVD and then you should be able to run Disk Utility and/or install OS.

-As well if you do not see the internal HD (macintosh HD) it means its not recognized by system and it needs to be repaired.

Hope this will help you out.

Are you sure your using the OSX discs that came with this mac mini? They are machine specific. Are you holding down the option key when trying to boot up the OSX DVD?

I have erased my Mac Mini hard drive using parted magic cd. look at http://www.partedmagic.com but you must download and create a cd, which can be tricky if your new at these things.

Also, what were you doing before this problem occured?

Mac OS X: Gray screen appears during startup

Symptoms

Instead of seeing the Finder or the login window after startup, your computer may stop responding and the display may only show a persistent gray screen (you may also see an Apple logo, spinning gear, spinning globe, prohibitory sign, or a folder with a flashing question mark on it).Note: The below steps may not apply if a blue screen appears during start up.

Resolution

Note: Some steps below may reset preference settings or registration settings.

Disconnect, test peripheral devices and network cables

Note: "Peripheral devices" refers to external devices other than what came with your Mac, such as hard drives, printers, or hubs that you connect via a USB or FireWire cable.

1. Shut down your Mac. If necessary, hold your Mac's power button for several seconds to force it to power down.
2. Disconnect all peripheral devices such as external hard drives or printers (leave only the display, a keyboard, and mouse connected).
3. Disconnect any Ethernet cables.
4. Start up your Mac.

• If you can start up this way, one or more of your peripheral devices (or installed software related to the device) is probably causing the gray screen issue. Connect one device, then restart your Mac to test for the issue. Repeat the process until you locate the device at issue. Make sure the device is powered if it needs to be to operate correctly. Check with the manufacturer of the device for support or possible software driver or firmware updates that may be available for the device. Try a different cable with the device if possible (such as a different USB or FireWire cable).
  Note: If you have multiple peripheral devices and the issue only occurs when they are all connected, but not when each device is the only peripheral connected, see the Additional Information section below.
• If you are using a desktop Mac with a third-party keyboard and/or mouse device, and the issue still occurs, try starting up with an Apple keyboard and mouse connected instead. Try starting with no keyboard and mouse connected, then connect them after start up. Also, try a different USB port on your Mac.

If the gray screen issue persists with no devices connected, go to the next section (with the peripherals still disconnected). Perform a Safe BootSimply performing the Safe Boot may resolve this issue.

1. Shut down your Mac. If necessary, hold your Mac's power button for several seconds to force it to power down.
2. Start your Mac, then immediately hold the Shift key. This performs a Safe Boot. Advanced tip: If you want to see the status of a Safe Boot as it progresses, you can hold Shift-Command-V during start up (instead of just Shift).
   
   Note: A Safe Boot takes longer than a typical start up because it includes a disk check and other operations.
3. If your Mac starts up as expected, immediately try restarting.

If the Safe Boot does not work, or the restart after a successful Safe Boot does not work, go to the next section.Reset the NVRAM / PRAM

1. Shut down your Mac. If necessary, hold your Mac's power button for several seconds to force it to power down.
2. Reset the NVRAM / PRAM.

If the gray screen issue persists, go to the next section. Start from your Mac OS X Install disc; use Disk Utility

1. Insert your Mac OS X 10.4 or 10.5 installation disc (if you have discs with both versions, use whichever is closest to the Mac OS X version installed on your Mac; do not use a startup disc which came with a different Mac or which contains an earlier version of Mac OS X).
2. Shut down your Mac. If necessary, hold your Mac's power button for several seconds to force it to power down.
3. Start up your Mac while holding the C key to start from the disc.
4. Once started from the disc, choose Disk Utility from the Utility menu.
   Note: If the gray screen issue persists and you can't start from the disc, go to the "Disconnect peripheral devices" section.
5. In Disk Utility, perform a disk repair of your Mac OS X volume; if no issues are found, perform a permissions repair as well. If issues are found during the disk repair, try repairing again.
6. After the Disk Utility operations are complete, restart without holding any keys.

If the gray screen issue persists, go to the next section. Check your cables and power sourceMake sure your power cables are secure (especially if you use a desktop Mac). Try a different cable or outlet if possible. If you use a surge protecter, try connecting directly to an outlet as a test.If you have power-related issues (such as your desktop Mac shutting down or restarting, or room lights dimming when an appliance comes on, consider contacting a certified electrician to check your outlets and electrical wiring).If the gray screen issue persists, go to the next section.Remove third-party RAM and internal hardware
Note: Skip this section if only Apple-brand RAM is installed in your Mac.Remove any non-Apple RAM or other third-party hardware upgrades (such as expansion cards or third-party optical drives or hard drives, if present) to help isolate the issue. This is necessary to get as close as possible to the original factory hardware configuration of your Mac.If you are not sure which RAM modules or other hardware is Apple or third-party, or if you are not comfortable performing these steps, or if you have a Mac mini, consider contacting an Apple Authorized Service Provider for assistance. Otherwise, perform these steps before going to the next section.

1. Shut down your Mac. If necessary, hold your Mac's power button for several seconds to force it to power down.
2. Open your Mac to access the memory slots. Refer to the User Guide that came with your Mac, or search Apple Support Manuals for a PDF copy of your Mac's User Guide.
3. Remove any third-party RAM that has been installed.
4. Reinstall the Apple RAM that came with the computer if available. Note that Mac OS X 10.5 requires 512 MB or more of RAM; Mac OS X 10.4 requires 256 MB or more of RAM.
5. If your Mac starts up with only Apple RAM installed, contact the vendor of your third-party RAM.

If the gray screen issue persists, go to the next section. Perform an Archive and Install installation of Mac OS XIf the above steps do not resolve the issue, and you can successfully start from your Mac OS X Install disc as noted above:

1. Insert your Mac OS X 10.4 or 10.5 installation disc (if you have discs with both versions, use whichever is closest to the Mac OS X version installed on your Mac; do not use a startup disc which came with a different Mac or which contains an earlier version of Mac OS X).
2. Shut down your Mac. If necessary, hold your Mac's power button for several seconds to force it to power down.
3. Start up your Mac while holding the C key to start from the disc.
4. Perform an Archive and Install installation (preserving users and network settings).

After installation, if the gray screen issue persists, go to the next section. Perform an Erase and Install installation of Mac OS X as a last resort
Important: You should only perform this step after trying all of the above steps. This process will erase all files from your Mac OS X volume. If possible, back up important files first, or use Time Machine. You may be able to connect your Mac to another Mac with a FireWire cable and FireWire target disk mode, in order to try to manually back up files. Alternatively, you may wish to make an appointment with a Mac Genius at an Apple store, or contactan Apple Authorized Service Provider for assistance.To erase your Mac OS X volume and reinstall Mac OS X:

1. Insert your Mac OS X 10.4 or 10.5 installation disc.
2. Shut down your Mac. If necessary, hold your Mac's power button for several seconds to force it to power down.
3. Startup your Mac while holding the C key to start from the disc.
4. Perform an Erase and Install installation of Mac OS X.
5. After installing, starting from your Mac OS X volume, and verifying the issue is resolved, you should use Software Update to update to the latest available version of Mac OS X.

Additional Information

If the issue persists after you follow the above steps, you may wish to make an appointment with a Mac Genius at an Apple store, contact AppleCare via phone, or contact an Apple Authorized Service Provider for assistance.If the issue only occurs when multiple peripheral devices are connectedIf a gray screen appears during start up only when several peripheral devices (that is, USB and/or FireWire devices) are connected, and you don't want to have only one device connected at a time, the issue may be caused by a combination of the peripheral devices.To illustrate this hypothetically, you may have three USB devices, which we'll call "A", "B", and "C". The issue may be that peripherals A and C have a conflict of some sort, and a gray screen only appears if they both are connected, but not if each one is connected separately. In the above "Disconnect, test peripheral devices and network cables" section you may have inferred that you have an issue only with device C because it was added after A. To avoid an inaccurate analysis, connect device C to your computer with no other devices. If your Mac has the startup issue with only device C connected, then you know it is the source of the issue. However if your Mac starts up, you have a conflict of devices to work out. To do this add the other devices one at a time with device C connected until your startup issue occurs (restart after adding one device). Repeat this process until you have just the minimum set of devices to produce your startup issue.What can you do?

• You should make sure each device has the latest firmware installed if applicable--check with the manufacturer for more information. You should also check for the latest driver versions, and if necessary install them while started in Safe Mode per above.
• If any of the devices requires a separate power source, be sure that power is connected to the device (for example, even if a device appears to be powered when connected via USB without the power cable, connect its power cable).
• Try different USB or FireWire cables with each device, as applicable.
• If you have a device similar to one of the conflicting devices, try replacing it with another one.
• Contact each device manufacturer or the materials that came with the device. for more support information or, if needed, service options