First thing I would do is verify the integrity of your hard disk. Go to the website of your hd manufacturer and download, burn and run their diagnostic utility. Alternatively, you can open a command prompt and type: chkdsk /r (then press enter). You will be told the drive is in use and asked if you want to run checkdisk at the next boot. Say yes, exit the command prompt, and reboot. If you have multiple drives or partitions, repeat the process for each (ie, for d: drive the command would be: chkdsk d: /r, etc). Note that there is a space after chkdsk and before the slash / switch.