Help with Upgrading to Windows 7 + Disc Checking?

I'm currently tring to upgrade to windows 7 from windows vista however the upgrade requires that I 'back-up' my files before upgrading, so I open up Windows Back Up and Restore and procede to follow the on-screen instructions. However, when it finally comes down to business an alert pops up stating "The Disc C: has errors. Windows has detected a corruption on C:. You must check the disc for errors before it can be restored." So I issue a disc check and restart the computer. The Disc check completes itself however when I attemp to back-up again I still get the same message. Is anyone computer saavy and can help me? Please keep in mind that I am computer illiterate. Thanks!