when it tries to boot n e thing it turns off

if i boot it from the onboard harddrives.. it shows a screen with a grey apple in the center.. then turns off.. if i boot it from the cdrom again i see a grey apple in the center of the screen.. then turns off.. seems like if it tries to boot to n e thing it just turns off.. i even tried swapping out harddrives and and even the cd rom... still the same result.. please help me..

Ok, we'd need some information though:

-What kind of mac is it? (iMac, Powerbook, iBook etc.)
-What model it is? (if you know) (iMac G3, iMac G4, iMac G5?)
-What OS was/is installed (OS 9/OS X)

mayby your holding the power button on too long

iWonder said:

mayby your holding the power button on too long

Click to expand...

If you hold it for more than 7 seconds it shuts itself back off.

power supply may be going? im not a mac tech, but a pc tech and to me it sounds like it could be one of 2 things.. power supply is going, or more than likely if mac's have this feature, its a Thermal Shut Down feature where if a Processor fan fails and it gets too hot, it shuts down to prevent damage.. just some suggestions...im probably way off but thought i would try..

Dennis