So earlier on this week, my 2x3.2 ghz quad core mac froze... was completely unresponsive, so I force shut it down. It re booted fine then after a few minutes its froze again... I shut it down again, it froze again. I left it for the night, switched it on in the morning, this time it froze on the start up. I tried booting it in safe mode, the progress bar went up and finished, then it froze. I tried booting it in holding down alt, this showed the HD and the disk that was in the drive, but clicking on either just froze it... I noticed that it did boot in target disk mode, so I borrowed my sisters macbook and connected them via firewire. When re-booting the macbook holding down alt it gave me the option of booting up on the 1st hard drive on my mac, I tried it and everything worked fine, all my files were still there, it was like i was on my computer... Then I got my sisters osx 10.6 disk and installed it on my hard drive via her disk drive/computer. This didn't appear to change anything I then opened up the side and there was a silly amount of dust, so I did my best to rid it of dust... then I swapped the hard drive in bay 1 for the one in bay 3 which still had plenty of space on it. Still all of the same problems... This is beyond me now, I guess (due to it not reacting to the swap) it cant be a hard drive problem that can be fixed with any erase an install procedures... what could be up with it? Is there anything else I should try at home, or should I get it seen to... any help would be massively appreciated thanks!