Orijinal gönderinin sahibi: ABCellars ,
Hook it up to an external monitor to help isolate the problem. If the artifacts are present on the external then the problem is hardware/video card related. The 7300GT has a known issue with the capacitors on the card. The 7600GT was also an option for your iMac. They cost a bit more but you may consider it a cost effective repair vs the 7300gt loto.