What is wrong with my iMac?

I have MacOSx version 10.6.8.
Processor 2.16 Intel Core 2 Duo
4 GB 667 MHZ DDR SDRAM
Graphic: NVIDIA GeForce 7300 GT VRAM (Total): 128 MB

It starts with lines located randomly on screen, black, or like monitor cracked. Then it happens like on screenshot - sprites of minimized window. I googled for similar problems and solutions, but haven't found satisfactory answer. It already went on service, but when it returned it continued with this problem. Can i you suggest some solution with installation of some program or driver or...?

skendzic said:

Can i you suggest some solution with installation of some program or driver or...?

Click to expand...

First thing I would suggest is booting from a Mac OS install DVD to see if the issues remain.

- Nick

Just based on your description, it sounds a lot like the GPU is overheating. This could be caused by dust build-up in the heatsink/ducts, or it could be a fan that is starting to fail. It could also be a breakdown in the thermal compound between the heatsink and GPU.

If you've already had it in for service and found their remedy to be ineffective, I think I'd be apt to haul it back in and tell them that it's not fixed.

I'll try to translate answer my collegue got from service:

"GPU burns out after 3 years - you need to change whole graphic card, because cooler is not on VRAM chips so they burn out in time. Price should be around 200 euros"

Anyway, thank you for answers, hopefully it will help people with similar problems.