UPDATE: I tried to re-install windows off of the Cd and I get this message:set up cannot copy pchdt_p3.ca_. ensure the disk labeled xp home edition cd rom is in the drive selected below or provide the location where the file can be found. It is supposed to be in I386,but it isn't. what gives?

 

I'm a bit late on this one but I would first clean the insides of all the dust bunnies that collect, make sure fans are clean. Reset memory (a pencil eraser works good to clean contacts).

Remove fan and/or heatsink from the processor, clean and reapply a thin film of thermal paste.

Almost every sudden start up problem I've seen have to do with heat or bad connections in memory.