Mac not booting

Hello there, Yeskay1.

It sounds like you are seeing a recurring Kernel Panic on your 2008 iMac computer. The following Knowledge Base article offers up some great, in-depth troubleshooting for recurring Kernel Panics:

OS X: When your computer spontaneously restarts or displays "Your computer restarted because of a problem."

In particular these sections may be useful:

Troubleshooting a recurring kernel panic

Diagnosing a recurring kernel panic can be difficult. If you need help with this process, consider bringing your Mac to a Genius at an Apple Store or an Apple Authorized Service Provider for help. If you plan to visit an Apple Retail store, you can make a reservation (available in some countries only).

Tip: To help diagnose recurring kernel panics, record the date and time it occurs, and any information that appears with the kernel panic message.

• Was the computer starting up, shutting down, or performing a particular task when the recurring kernel panic happened?
• Is the kernel panic intermittent, or does it happen every time you do a certain thing? For example, were you playing a particular game, or printing at the time?
• Does it occur only when a certain external device is connected, or a device is connected to a certain port?

Isolate hardware or software as the cause of the issue

To try to figure out if the issue is related to software or hardware, use the computer with a fresh installation of OS X on an external drive.

1. Start the Mac from OS X Recovery.
   If a kernel panic still occurs when started from Recovery, there is likely a hardware issue. See the "Hardware troubleshooting" section below for additional information.
2. Open Disk Utility and use "Repair Disk" on your Mac's internal hard drive (named Macintosh HD by default).
   
   Important: If Disk Utility is unable to repair the internal drive, you should back up your important data immediately and if possible, reformat the drive. Consider bringing the Mac to a Genius at an Apple Store or an Apple Authorized Service Provider for further diagnosis. Be sure to ask that, if the drive needs reformatting or replacing, they contact you about escalating your case to a special data recovery service. If you plan to visit an Apple Retail store, you can make a reservation (available in some countries only).
   
3. Connect an external drive with at least 10 GB of free space. Note: Make sure the external drive does not cause kernel panics, and is the only device on its USB, FireWire, or Thunderbolt port. Connecting the external drive and its cables to another Mac can help make sure the drive does not cause kernel panics.
4. Install OS X on the external drive.
5. Start up from the external drive.
6. Use Software Update to install all updates until it reports "Your software is up to date."
7. Don't install additional software on the external drive, but instead use the Apple applications to surf the web, view QuickTime movies, email, print, scan, and/or other activities. Continue using your Mac for the amount of time it would usually take for the issue to occur.
8. If a panic occurs, select the "Hardware troubleshooting" section below to further diagnose the issue.
   If a panic does not occur, select the "Software troubleshooting" section below article to further diagnose the issue.

Hardware troubleshooting

Disconnect the external drive used in the above test to determine if the kernel panic is due to a hardware issue.

Check peripheral devices first

Go to the next section if you have no devices attached to your Mac.

1. Turn off your Mac.
2. Disconnect all peripheral devices. If you have a desktop Mac, make sure all you have connected is a display and Apple keyboard with Apple mouse or trackpad.
3. Turn on your Mac.
4. Use your Mac for the amount of time it would usually take for a kernel panic to occur.
5. If a kernel panic does occur: Proceed the next section to check the internal RAM and third-party hardware.
   If a kernel panic does not occur: Power down the Mac and connect one peripheral device at a time and test until a kernel panic occurs.

   Note: A combination of peripherals may be the cause of a kernel panic. Disconnect one peripheral at a time to see if it causes a kernel panic by itself. If the kernel panic does not occur, continue to add peripherals until you find the other peripheral needed to cause the kernel panic.

Check internal RAM and third-party hardware

1. Turn off your Mac.
2. Reseat the Apple RAM, and remove third-party RAM and third-party internal hardware. If you do not have the Apple RAM that came with the system, reseat the third-party RAM.
3. Turn on your Mac.
4. Use your Mac for the amount of time it would usually take for a kernel panic to occur.
5. If the kernel panic does not occur: The third-party RAM or internal third-party hardware may need to be replaced.
   If a kernel panic does occur: Bring your Mac to an Apple Store, or an Apple Authorized Service Provider for service and support. Be sure to ask that, if the drive needs reformatting or replacing, they contact you about escalating your case to a special data recovery service. If you plan to visit an Apple Retail store, you can make a reservation (available in some countries only).

Software troubleshooting

Disconnect the external drive used in the above test to determine the kernel panic is due to a software based issue.

1. Start the Mac from OS X Recovery and reinstall OS X on your Mac.
2. Start from the installation of OS X you just created.
3. Use Software Update to install all updates until it reports "Your software is up to date."
4. Download and install any third-party software updates before reinstalling third-party software, especially drivers and kernel extensions.
   Examples include:
   • Virtualization software
   • Drivers for add-on third party display cards
   • Anti-virus software
   • Networking software (especially software which enables third party network devices)
   • Add-on file system support software; for example, software that lets your write to NTFS formatted media.

If the issue continues, you will need to erase and install OS X as follows:

1. Start the Mac from OS X Recovery.
2. Complete a disk image backup via Disk Utility of the internal drive to an external drive with enough free space.
3. Erase the internal drive using Disk Utility.
4. Install OS X.
5. Start from the internal drive.
6. Use Software Update to install all updates until it reports "Your software is up to date."
7. Re-install your third-party apps and copy your user data from the disk image backup you created in step 2.
   Note: Avoid copying data from the /Library and /System folders on your backup disk image.

Advanced information about kernel panics and panic logs

You can check kernel panic logs for more information. The kernel panic text is added to the log after you restart the computer, assuming that you did not reset PRAM (the kernel panic text is stored in PRAM until you restart). In Mac OS X v10.6 or later, the logs are located in in /Library/Logs/DiagnosticReports.

Information that may aid developers in the investigation of a software issue may be in the log. The information may also provide clues as to what may have caused the kernel panic.

Understanding and Debugging Kernel Panics – This technote addresses kernel panics: what they are, how to read panic logs and how to debug the code that caused the panic.

Kernel Core Dumps – This technote explains how you can enable remote kernel core dumps used to collect data about the kernel panic.

Note: If you are a software developer, booter settings and debug flags may cause different symptoms for kernel panics.

Thanks for reaching out to Apple Support Communities.

Kind Regards.

From what you describe an mistake in entering that command erased everything, possibly on all mounted volumes.

Assuming you have no backup from which to recover, reinstall OS X. You will need that Mac's original, grey, System Install DVD, a retail Snow Leopard DVD, or suitable alternative means of installing a compatible operating system.

Glad to hear. Thanks for the update.