is it ok till the machine warms up then I would suggest a heat problem.
He needs to have a look inside for starters to check all fans are spinning. AGP Graphics, CPU HSF, PSU has 1 or 2 fans inside just shine a torch in grill (Do Not open PSU)
Then I would run a HDD test, I have seen HDD's when they get warm and have a fault they freeze
Then I would run CCleaner, Stinger, CW Shredder
Check all windows updates.
Thinking about it, has he just got the Windows XP SP 2 installed this could be causing a compatibilty issue with other software or Hardware.
Think there is enough to go on for now but call back for more.