Disk Cleanup in Win XP

Ever since I got my PC, pre-loaded with Win XP Home Edition, I have not been able to use the “Disk Cleanup” utility. I click on button, the program starts, and then simply hangs – every time. I have waited at least an hour (it is a 40GB HD) but still nothing is happening. I have had to resort to deleting files manually every now and then, but I really would prefer to get this thing working as it should.

Any ideas?