It's Not unusual for 'Defragmenters' to stick. Anyway, Modern Operating Systems such as Windows 7 do Not benefit from Defragmenting; which is a waste if time.
What I am saying is that you Do Not need to Defrag. Perhaps you are able to tell me why you think you need to do Defrags. If it's to speed-up your equipment, I doubt whether you will notice any difference.
Defraging was perhaps useful 20 yrs back when Storage space on Hard Disc Drives was very small as compared to today.
Either 'My Computer' or use Windows Explorer. Find and right click the drive. Select properties. The general tab shows used & free space. Defrags can have problems if there is a lack of free space to move things into and out of.