It's either a failing hard drive, or corrupt data coming in from failing RAM. Most likely is hard drive, but you can test the RAM using a free program called memtest86 available online. To avoid using the hard drive you'd want to boot the memtest from a USB thumbdrive, or from a CD.

Next thing is to run chkdsk /r/f on the drive, then check the Events area and see what it put there as the results of that. What you are looking for is it finding "bad sectors" or failed sectors.