Checking Windows files and the hard drive for errors
Open Windows Explorer. In the left hand pane click on the "+" next to My Computer. Right click on the icon for the "C" drive, it might be called "local disk". Select "Properties" from the list that appears You are now looking at the "General" tab, click the "Tools" tab.
Click the "Check Now" button and wait until Windows has finished checking the disk. It will tell you when it's finished. There will be 3 phases for NTFS and only 1 for FAT 32, don't worry about the jargon, just let Windows do it's job.
If Windows cannot finish the check it will display an error message to that effect. This usually means trouble, either the Windows files are damaged or corrupted or worse, the hard drive may be damaged.
Try the "Automatically Fix ... errors" click "OK" then click "Yes" on the pop-up and restart the computer.
When the computer restarts, Windows will check it's file system and will attempt to correct any errors. After it's finished the computer will restart normally.
Do not click "Scan for .... bad sectors" unless you are prepared to leave the scan running for hours. If you do scan for bad sectors leave the computer alone for as long as it takes. If you switch the computer off you will cause even more damage to occur.