Disk Defrag Doesnt work.......

So, im trying to once again run disk defrag. It hasnt worked in a couple
weeks. What happens is i start it up, it runs the "anailzing disk" part and i
can see my HD run for a min or so. But then it stops and thats it, i left my
computer alone for like 6hrs, and when i came back, it still said "anailzing
disk".

ANyone got any help on this. When i goto task mgr, i see it in there, but i
cant end the process, i have to reboot.

So what happened, why does it get stuck at the "anailzing disk" part and not
go any futher

thanks