I've got a 2005 iMac G5 PowerPC 1.8GHz running Leopard. It's been running absolutely fine since I had it (upgraded to Leopard for at least 18 months) but randomly a week or two ago it's started crashing. Sometimes two or three times in a row, then it's been 2-3 days without problem. The display starts flickering, usually the mouse pointer can still be moved but after 10-20 seconds or so it will just crash and I have to restart by holding the power button down. There's nothing in the crash log. I've run the hardware test and checked the memory and everything is looking fine. I've completely reinstalled Leopard and also cleaned out the fan in case it was overheating that was causing this. Managed to take a few screen grabs. Any ideas? At a loss as to what's causing this.