I recently bought 1 2gb DDR2 stick of ram to replace my old two 512mb sticks. I installed it and immediately had problems with my computer restarting at any time, despite my computer booting up and loading programs faster when it boots. My motherboard is a 775Dual-VSTA and is compatible with 2 gb DDR2 RAM.
I also had problems installing Fallout 3 - my computer would restart when it got to a certain point in the installation. The computer would also restart when I transferred big files in between hard drives. I thought it might have been the RAM slot I put the RAM in, so I switched it into the other slot, and instead of the computer restarting it would just freeze. When I moved big files again, the computer would freeze and the mouse wouldn't move, and the computer wouldn't recognize any keyboard inputs. This also happens periodically when I use firefox.
I was actually able to install Fallout 3 now, but the in-game video cutscenes are very choppy, and the game freezes 30 seconds into it. I am having the same problems I had on the desktop - no mouse or keyboard input at all.
My next step is to run memtest to see if the memory is faulty (which I doubt, it's brand new). I am thinking I don't have enough power, or the RAM is getting too hot.
I can post my dxdiag if necessary.