Windwos XP Professional Help Please.....

I recently bought a copy of Windows XP Professional and I am having only one probmlem with it (yay becuase Windows ME was always crashing)...anyway. When I try and run Norton Disk Doctor or Windows Scan disk a problem comes up that says it cannot repair files becuase windows need exclusive access to certian files and said I should reboot the computer to fix the problem, I reboot and the same problem happens next time I try and run either of those applications. Any ideas on what I should do?