Mac Won't Boot and then Shuts Down!

[MacBoy200]

Hi everyone,
I have been having this problem for 3 weeks now.
Pretty much, when I boot up my (desktop) iMac, it will go to the grey screen, then to the grey screen with the apple logo. Normal stuff.
BUT then a grey loading bar appears at the bottom of the screen. It will load a tiny amount, and then the computer shuts down. This whole process takes about 3 minutes. Please help!

 

[RedCroissant]

Hi everyone,
I have been having this problem for 3 weeks now.
Pretty much, when I boot up my (desktop) iMac, it will go to the grey screen, then to the grey screen with the apple logo. Normal stuff.
BUT then a grey loading bar appears at the bottom of the screen. It will load a tiny amount, and then the computer shuts down. This whole process takes about 3 minutes. Please help!

Which iMac is it? Did you recently upgrade anything..HDD or RAM? This could be caused by RAM that not properly seated. Try making sure the RAM is in there correctly and then try again.

 

[forty2j]

Grey Bar, when it happened to me, meant the HDD needed repair. Boot off a recovery partition or OS X CD and run the disk utility.