press the start button, type "cmd". Right click "cmd.exe" and select run as administrator.
Command prompt should start; type "chkdsk /r" and press enter. It will likely ask you if you want to dismount- say y. it will likely then say the volume is in use, yadda yadda, "do you want to schedule this disk check for when the system is rebooted?" or something along those lines. Say yes to that as well.
Once you finish that, reboot. Note this will take a LONG time, in the area of several hours, depending on hard drive size.
