wont start up...

Try starting up in "Safe Mode"...hold the shift key down when you hear the start tone. If it boots, repair disk permissions then restart.

If it will not boot in "Safe Mode" then you need to try "Single-User Mode" hold the Apple/Command + S
down. This will result in a black screen with white text. When you get a boot promt...#
enter this

/sbin/fsck -fy (press enter)

This repairs the startup disk. When finish type in

reboot (press enter)

If it boots up, repair disk permissions.

Hope this helps...Cheers,
Glynn

Try booting in Safe Mode without using Terminal commands.

http://support.apple.com/kb/HT1455

Have you tried booting from your install disk?
Insert the installer disk and Restart, holding down the "C" key until grey Apple appears.
Go to Installer menu (Panther and earlier) or Utilities menu (Tiger and later) and launch Disk Utility.
Select your HDD (manufacturer ID) in the left panel.
Select First Aid in the Main panel.
*(Check S.M.A.R.T Status of HDD at the bottom of right panel. It should say: Verified)*
Click Repair Disk on the bottom right.
If DU reports disk does not need repairs quit DU and restart.
If DU reports errors Repair again and again until DU reports disk is repaired.
When you are finished with DU, from the Menu Bar, select Utilities/Startup Manager.
Select your start up disk and click Restart






Carolyn 🙂

You have to click the Repair button.

You need to take your iMac in for service. 😟