I had the same problem albeit on Windows 98SE. It seemed to be very much temperature dependant in that in the warm weather (over 62 deg.F) it didn't freeze. If I restarted the computer after letting it run for a few minutes it was ok. It appeared to be faulty hardware and a new hard disk cured it. It still occasionally does it, when it does I shut down and restart - it starts in safe mode and when I select "normal start" from the options it loads ok.
Assuming with a computer that new then you'll be running Windows XP so maybe it's worth using system restore to go back to a point when it doesn't happen - have you installed anything that may have caused it?