Q: Imac Stuck on grey apple screen

1) You should run disk utility.  You'll need to do this from your 10.5 dvd.

     a) verify the disk

     b) update your permissions.

2) Try a safe boot.

    Shutdown your machine.  Hold down the shift key.  Poweron.  Wait awhile Wait awhile while you harddrive

      is being checked.

    http://support.apple.com/kb/ht1455

I suspect disk corruptions.

verify & repair your startup drive

To verify & repair you file system on the startup drive, you will need to run disk utility from you installation DVD.

This article  will tell you how to get to disk utility.  Once in a disk utility, you can go and attempt to recover the disk.

http://support.apple.com/kb/TS1417

To repair your startup drive, you will need to run disk utility from your startup DVD.
Mac OS X 10.4: About the utilities available on the Mac OS X 10.4 Install DVD

http://support.apple.com/kb/HT2055

How to run disk utility from your startup DVD.

1. Insert your  startup DVD  into your reader.  Power down your machine.  Hold down to the c key.  Power on your machine.  This will bootup your startup DVD.
2. This will bring you to a panel asking you for your language.  Pick your language.

        

3. You you come to the Install Mac OS panel.  Do not install.
4. Click on Utilities menu item.  This will give you a pulldown list of utilities.
5. Click on the disk utility.
6. You are now in disk utility.  Pick your disk.  Click on repair it should be on the lower right of the panel.
7. Once the repair completes successfully, you should update your permissions.

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Verify a disk

As an alternative, you can verify that the filesystem on the disk is correct. You will not be able to repair the file system.

I suggest that you use disk utility to verify that your startup disk is OK. 
Macintosh-HD -> Applications -> Utilities -> Disk Utility 
Start up disk utility.  On the left pane view, you will see a list of all your disks.  
Click on your startup disk.
Click on the First Aid  Tab.
Click on verify.  

Hopefully your disk will verify.  If not, you have to boot from your installation DVD and run Disk Utility from there to attempt to repair your file-system.

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Before buying anything, try to verify hardware.

Try a safe boot.

    Shutdown your machine.  Hold down the shift key.  Poweron.  Wait awhile Wait awhile while you harddrive

      is being checked.

    http://support.apple.com/kb/ht1455

Try holding down the option key then power on. This brings up the startup manager. Click on your hd. Click on right arrow key.  [ You should at least get the startup manager. ]

This should work.

Sometimes if volumes don't appear in Startup Manager (what you get when you hold down the Option key at startup), you need to reset the Mac's PRAM, NVRAM, and Open Firmware. Shut down the Mac, then power it up, and before the screen lights up, quickly hold down the Command, Option, P, and R keys, until the Mac has chimed twice more after the powerup chime. Then, before the screen lights up, hold down Command-Option-O-F until the Open Firmware screen appears. Then enter these lines, pressing Return after each one:

reset-nvram

set-defaults

reset-all

"The reset-all command should restart your Mac. If so, you have successfully reset the Open Firmware settings."

http://support.apple.com/kb/TS1812?viewlocale=en_US

How to eject a cd from the internal cd drive:

eject cd

List of devices:

devalias

List of variables:

printenv

( nvram is the equivalent Mac OS X terminal command. )

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Resetting your Mac's PRAM and NVRAM

http://support.apple.com/kb/HT1379

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reset the PMU

http://mrjcd.com/junk/PMU.jpg

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Don't get your hopes up, but ocasional Apple seems to find a few discs in a back closet.

Apple may still supply the original restore CDs/DVDs for a nominal fee.  Have your serial number and model information available when you call them. You do not have to be the original owner.

AppleCare Support Phone Number: 1-800-275-2273

open 6am to 6pm Pacific Time

Apple Phone Sales 1-800-692-7753

International Technical Support Numbers

http://www.apple.com/support/contact/phone_contacts.html

"You have to call Apple & likely ask for a Product Specialist to get it (Leopard), if they still have it... helps if you tell them you have a new iPhone (iPad) that needs it!"

BDAqua

Requirements for Mac OS X v10.5

http://support.apple.com/kb/HT3759