iMac G5 (no iSight) display problem

Computer: iMac G5 (no iSight) with 2.0 GHz, 250 GB HDD, 1 GB RAM, 128 VRAM bought in August 2005.

Problem: Around December 2008, the display went black after reboot/awaking from sleep; however, the computer itself is running. I have tried the following:
1. Reset SMU
2. Reset NVRAM (this used to work quite well up until today)
2.1 Repaired permissions, Techtool Pro booting from CD to fix issues, but none are reported and problem persisted.
2.2 Went to the Apple Geniuses who hooked it up to external display and switched display from external to internal. This worked to restore my display but rebooting or putting display to sleep brings back the black screen. Being out of AppleCare warranty, he recommended to upgrade from Tiger to Leopard.
3. Upgraded OS from Tiger to Leopard with updates and problem began again.
4. Googled until my eyes fell out...

Every time I get the computer to display correctly - that is via multiple NVRAM resets and cursing - I cannot reboot or put it to sleep without recreating the black screen.

Since, in the Apple store, the Genius changed the display settings via external display and I got my screen to display properly, I figured I could do the same with Screen Sharing. I hooked up my new MBP to my iMac via Screen Sharing in hopes of being able to reset the display settings. Screen sharing works like a charm but the iMac does not think there is an external display hooked up (which there, of course, is not). I am now out of ideas.

I will run some tests of TechTool Pro via Screen sharing and then downgrade to Tiger and avoid doing the updates.

Extras: It is likely that an apple update caused the issue but I cannot prove this. I do not have apple care and have called Apple and gone to the apple store and they are not budging on helping me out with free repairs - logic board replacement is seriously expensive but I do not think it is LB issues as I can view my display via Screen sharing and when I get the display to function properly, I have no problems at all... Apple, you have stumped me!

Please let me know if I need to expand or improve my explanations.

 

Besides the fact that buying a new computer will fix ANY problem, I am more interested in finding a solution to the current problem. There has to be one. Is the iMac G5's video card removable or integrated with the Logic Board?

I don't think the problem is impossible to fix - i.e. not a permanent hardware problem. Why else can I get the display to work sometimes?

Also, using an external display will work too.

 

Quick Update: Upon thrashing iStat Nano (based on online threads) and installing TechTool Pro 4 from the DVD and performing the installer's required restart -- all via Screen Sharing, the iMac booted up correctly by itself. Even putting it to sleep now brings back the iMac correctly. Let's see if the computer can get past the usual three days of working properly.