Blue Screen except on Safe Boot

Question

I have been struggling with my iMac for the past few days. The other morning I started it up and it got hung up on the "blue screen." I have tried various things:
- Resetting PRAM
- Unplugging power and hitting power button, then plugging back in and restarting.
- Tried to start from Leopard DVD (10.5) <By holding 'c' while starting>, but unable to get past "blue screen."
- Tried to start from Tiger DVD (10.2), but unable to get past "black screen."
- ABLE to start in "Safe Mode" <By holding 'shift' while starting>
- While in "Safe Mode" I was able to "Repair Permissions" but still got "Blue Screen" when I restarted.
- Tried to use "Time Capsule" while in "Safe Mode," but the system got hung up.
- I do NOT have "Application Enhancer" on my computer.
I am at a loss on what to do and cannot seem to find anything online which would seem to indicate that others have had this problem.
Message was edited by: jedioliver

Answer 1

Welcome to Apple Discussions,
- Tried to start from Leopard DVD (10.5) <By holding 'c' while starting>, but unable to get past "blue screen."
- Tried to start from Tiger DVD (10.2), but unable to get past "black screen."
- ABLE to start in "Safe Mode" <By holding 'shift' while starting>
iMac G5 1.8GHz 768MB
I would try booting from those install discs by using the holding down the Option key and then explicitly selecting the install disc, so that you know for sure that you have not just rebooted from the internal HD again.
Assuming there is no change, you can sometimes see this very puzzling behavior if there is a video hardware problem, unfortunately quite common in iMac G5s - see this thread in the iMac G5 forum:
*Only working in Safe Mode*
http://discussions.apple.com/thread.jspa?messageID=11119348
A possible explanation is that one of the features of Safe Mode is that it "loads only required kernel extensions." If there is a faulty hardware component that is only needed for "enhanced" performance (like fancy video/graphics), that component might cause a crash when a normal boot loads the special kernel extension that calls upon it. A Safe boot could conceivably bypass this faulty hardware by not loading that specialized kernel extension.
Sometimes, but not always, such hardware faults are detectable by running Apple Hardware Test, which is on one of the original install discs that came with your computer - see your instruction manual if you still have it. If you don't, running AHT depends on which model iMac G5 you have. You mentioned Tiger DVD (10.2), but Tiger is OS X 10.4. If it's a first generation iMac G5 it came with Panther (OS X 10.3) , and AHT will be on a separate bootable disc labeled “Additional Software & Apple Hardware Test”. If it is a second generation model it probably did come with Tiger, and AHT will probably by on Install Disc 1- hold down the option key while booting from it.