If you mean that you try to start Disk Cleanup and it opens but just sits there, it's probably freezing on the "Compress old files" attempt. I usually just disable that from the outset since it seems to be problematic.
To disable it,
Click Here to open Kelly's Korner.
Scroll down to line 48 and in the right-hand column, click on "Disk Cleanup-Compress Old Files Freezes" to download a small .reg file. You may have to right click it, left click "Save Target As" or, if using Firefox, "Save Link As."
Once you've got it saved to the hard drive, run it according to the instructions at the top of the Kelly's Korner page.