Unless you ran AHT in Extended Mode at least 2-3 times back to back you really didn't run a comprehensive test. Even then AHT isn't the most reliable solution. Run AHT 2-4 times in Extended Mode back to back, if it doesn't show any errors take the machine in for professional diagnostics. Of course do this after doing both iMac SMC and PRAM resets and restarting in Safe Mode to clear some caches.
Well, gave the extended AHT 4 consecutive tries. Each time, it said that everything appeared okay.
So, guess I'll continue to get by with Safe Mode until I have the $$$ to get it diagnosed/repaired. Or, maybe some fine day, a whole new Mac. Something to look forward to :-)
Have a good one...
The Safe Mode restart is very simple to do, when you hear the startup tone hold down the Shift Key until a progress bar appears. Let it fully boot then restart normally and test. If they problem continues then my guess is it's a hardware issue. If you still have AppleCare on it this should be covered.
It restarts okay and does what it's able to in Safe Mode. That's what I've been doing for a while, now.
Sure would be nice to have a fully functioning iMac again, though.
AppleCare is way in the past at this point. One of these days, I'll take it to an Apple Store and let them have a go at it. Or, at least give me the (bad) news as to how much it'll cost.
If it should turn out to be the graphics unit (been reading less than complimentary things about Nvidia 8800 gs), any estimate on what Apple might charge for that sort of repair? If not, no worries. Guess I'll find out soon enough.