Mostly likely you have a problem in memory or HDD. Before you go swapping components, however, try booting into 'safe mode' If that doesn't work, and you have tried two different OS's then you definately have a hardware problem. It can be a bad sector on the HDD, a bad memory location, or bad cache on the processor. It is possible that it is the motherboard, but unlikely in this case. There are freeware tools that will allow you to check memory, bit by bit, as well as HDD sectors. It will be a time consuming battery of tests, however. Good luck.