If defrag doesnt run,a repair will not fix the problem.Read kb article:
http://support.microsoft.com/kb/922379
"Socrates" wrote:

> I have windows xp home edition. I have been trying to defrag my hard disk now
> for a few months but the box keeps coming up "greyed out" showing the bars
> etc with no instructions visable and the buttons won't respond. I have
> tried various ways to cure this problem including "disk cleanup" and starting
> in safe mode etc, but without success. I am reluctant to reinstall windows xp
> in case it will lose important work / files /software on my computer. Is
> there another way to make my defragmenter system work? Any help and advice
> would be much appreciated.
> --
> plato