This problem has just cropped up a few weeks ago.
After a shut down and/or restart, upon start up, XP will boot normal to the welcome screen.
After clicking on a user the 'restore active desk top' message will appear on a white background usually but not always.
Then, after a little bit, it freezes and nothing works.
Two or three restarts gets it back working. The desk top however has to be restored through; control panel>display>'OK'
I have tried;
Deep scan with Trend Micro I.S. & Registry Mechanic.
Deleted all temp folders & cookies.
Anything else I should try?