Recurring Freezing Win XP

I am having problems with recurring freezing, though I can't seem to find a pattern.

I will sometimes get 4+ hours of computing, using everything from World of Warcraft to multitasking with Photoshop, Word, Firefox, etc.

Once I do have a freeze up, in which case the mouse will seize and the screen will freeze requiring a reboot. On reboot it is sometimes VERY hard to get WinXP to boot - sometimes it will get stuck on "welcome", sometimes earlier, occasionally it will boot all the way to desktop and I have 2min or so of runtime, then it freezes again.

Usually the system will eventually boot and work, but sometimes it takes many restarts. Also, sometimes if I just let it be when I come back an hour later it will boot fine. All fans are working, and the hardware monitor has my CPU etc. well under the warning temps...

The powersupply, memory, GPU are relatively new.

Any suggestions?

Thanks in advance!

 

I would start with a memory testing program such as this, http://www.majorgeeks.com/Memtest86_d4226.html. Then I would use the Hard Drive manufacturers diagnostic tools to check the condition of the hard drive.