I too think it's a memory problem.
After running memtest86 for years, I've just been given a better, Microsoft BETA VERSION, one. It takes <2 minutes to download from here click here and about 10 minutes to run, depending on how much memory you have.
Save it to the hard disk, double click it, accept it and point it to save to a floppy.
To run it, reboot (restart will work) your computer with the floppy in the drive. After the reboot, it will load and the first test pass will begin using the standard test suite, and continue until complete, unless it is either paused or exited. Once the first test pass is complete, it will begin a second test pass, third pass, etc. ad infinitum.