Unable to run scandisk- Win XP Pro

I go to run scandisk, with fix errors box checked, & I get a msg that a process has access to the drive and that scandisk cannot fix errors. This didn’t used to happen, wonder if the NAV product could be doing this? The system is: NEC GT100, 450mhz, 256Ram, XP Pro (upgrade from 98SE), trying to make a dinosaur live a little longer before extinction! How can I determine what may pgm or process has access to the drive, and safely stop that process from starting, so I can fix any errors on the drive? I believe that I have tried unchecking the fix errors box & running scandisk at startup, don’t think that I was able to fix errors however. F1,F1!