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Step 1:
Run disk clean up.
It removes temporary files, empties the Recycle Bin, and removes a variety of system files and other items that you no longer need.
http://windows.microsoft.com/en-us/windows7/Delete-files-using-Disk-Cleanup
Step 2:
Follow the steps below.
a. Click Tools, open Folder Options , choose View -- temporarily Uncheck Hide Protected Operating System Files.
b. Then on the Explorer C: (root) drive find the folder $Recycle.bin .If you don't see it, close and reopen Explorer.
c. Right click on that and delete it.
d. You may get some message about its being corrupt or warnings about .ini files.
e. The bin should temporarily disappear from the folder tree.
f. Delete a file and it should reappear again.
g. At this point you can recheck the "hide protected operating system files" option in View.
Step 3:
Run Check disk for errors. You may refer the below mentioned link for more information and steps for check disk.
http://windows.microsoft.com/en-us/windows7/Check-a-drive-for-errors