1. To run chkdsk, click the Windows Orb (Start) > All Programs > Accessories and right-click Command Prompt, then ‘Run as Administrator’. Type chkdsk /r (note the space) and press Enter. It will probably run next time you restart the system, which you should do now.
2. You haven’t actually said what the prefetch error message was, but this will solve a ‘Not working’ message. Click the Windows Orb (Start), type %SystemRoot%\Prefetch and press Enter. Now delete everything that appears.