I've got a Windows 7 machine that is locking up randomly. It can be in the first thirty seconds, or it can be hours later. There is nothing specific I can find that is running when it happens. When it locks, the screen doesn't change, but nothing moves. The waiting icon stops, the mouse stops, keyboard doesn't work, etc. I've even tried the crash on ctrl-scrl registry hack, and it won't even dump the kernel. I've run hardware diagnostics on the RAM and it doesn't find any problems. I would think it is a hardware issue, but on this exact same machine, I can run 64 Bit Ubuntu and it has zero problems. I've even tried reinstalling Windows7 from scratch, and it still happens.

Anyone have any ideas? Any good diagnostic tools to recommend?

Thanks! Michael