One thing you may want to try out is the chkdsk utility the next time you boot the system. As soons as the post tests come to an end you press the F8 key to enter into the boot menu. On some boards you may have to wait a little longer to get past the menu to choose which drive to boot from. In the menu where you would choose between the normal startup, safe mode, and the last know configuration that worked options you would choose the safe mode with command prompt only option. Once at the prompt you would type "chkdsk /f" or "chkdsk /r" to see if that will locate and repair any errors found on the drive. It sounds like that could help there.