1) Where's your dmesg? That would show which kernel and which architecture you are running, as well as more details about your hardware which you have yet to provide.
2) How many hours did you run memtest86?
3) What do you mean by "locking on me" ?? e.g.: does this occur while running X on in console? If in console, can you switch to another console via keyboard? Can you log on remotely? Does the platform respond to pings?
A little information goes a long, long way, ddocksta. While nobody's perfect, please read
http://daemonforums.org/showthread.php?t=596 for what we'd like to see.