Make sure to do a clean boot and make sure the AV is off. Also if you havent done so yet make sure to do a bad sector check on the drive as well. Open a cmd.exe window as administrator and type in
chkdsk c: /r
It will say it cant and would you like to at next boot, hit Y and enter and then reboot. Before windows starts it should start the chkdsk, and it will take a while!
Shane