I have two users A and B. I am logging on as user A. I used to switch to user B.So far, so good. The problems start when I decide to go back to user A either using logging off B or switching (again) to user A. I came upon to a black screen (the power is on) and nothing is done.
From the XP discussion groups I discovered UPHClean(Microsoft hotfix), I 've installed it and the problem has been fixed partially. Now,I can switch back to user A from user B but not logging off user B and return back to user A. Again the beautiful black screen...
I'd appreciate your help.

When you are on the black screen, press CTRL + ALT + Delete.
Click on File - New Task. Type explorer.exe