Just Another Thought...
Occasionally, there are issues with files and the drive which can be corrected with the "Chkdsk" utility.. First, delete all junk files such as those in the Temporary Internet Files folder and all the "Temp" folders.. Once that's done, run a Disc Defrag if you haven't in a while.. Once that's done, run the Chkdsk utility using the instructions below:
Click on Start-Computer to see the various drives in "My Computer". RIGHT click on the "C" drive listing, choose "Properties" from the list, then click on the "Tools" tab, then click on the "Check Now" button in the "Error Checking" section.. When that opens, place a CHECK mark in both boxes listed there and click on the "Start" button. You'll then receive a popup indicating that Windows can' run the scan while it's in use, SO....click on the "Schedule a disc check" button. Once that's done, restart the computer and Chkdsk will run when it boots up.. THIS SCAN WILL TAKE AN HOUR OR MORE....so please don't turn off the computer till after the scan is finished.. If you've not done this before, the scan will show a DOS type screen, not a typical Windows display.
Hope this helps.