xp cpu upgrade problems

Hello, this is my first post ever on THG. This is a really long problem so just please bear with me. Yesterday I just upgraded my homebuilt pc to an Athlon XP 1900+ Processor from a 1.0Ghz thunderbird.
The rest of my system specs are:

Noise Control Silverado (12v)
DFI Ak-76-SN
256MB Crucial DDR 266 CL2.
Western Digital Caviar 15.0 GB ata 66/7200rpm
Hp 8x12x32 cd burner
Creative labs 16x DVD
Sound Blaster Audigy Platinum
Asus TnT2 Ultra
Kingston Ethernet (model 120 something)
Aopen 250w Athlon approved power supply
Win2k sp2

All I changed from the previous configuration was the processor. The system will usually boot normally and runs at a normal temperature (95-107F). When I get into windows is where everything falls apart. Sometimes after I log in a blue screen appears with some random error message. Most of the time however I can get to the desktop and everything is fine. I can watch DVDs, listen to mp3s, and write emails to my hearts desire with no problems. The problem seems to be caused when I start up Seti@home client. After 15-30 seconds the system will lock up, reboot, or blue screen then reboot. So I tried another program to put my processor under 100% load and the same thing happened. Before the upgrade I never had problems with my system. Do I need to give my new CPU some break in time before I put it under 100% constant load? Or is there something else here that I am missing? BTW I always make sure that I have the latest drivers, updates, bios verisons, and latest Norton virus files.
<P ID="edit"><FONT SIZE=-1><EM>Edited by Rainchill on 05/04/02 01:35 AM.</EM></FONT></P>

Crashmans right your power supply is not adequate.

Thanks guys. I can't believe I didn't think of this one. I unplugged all unnecessary disk drives and took out all the cards I could. It has been running for 3 hours under 100% load.

Did you reinstall your OS?

"Just the facts ma'am"