Running Scandisk

HI

I need some help about scandisk. I cann't run a full through scandisk operation, it keeps restarting. I have tried turning everything of in the background that I can find, and it still says that windows is writing to the disk. Is the some trick that I am missing or does anyone know of a good third party(hopefully free) program that does the same thing as scan disk. I need this done because when I go to defrag. it says that I need to run scandisk first.

Any help and ideas would be great

Thanks