Upgrade Celeron D to a Pentium D = CRASH

[myequation]

MOBO: Gigabyte 8I865GME-775
RAM: 1g kingston dual channel 400mhz
PSU: tHERMALTAKE 500W W0120
full psu specs at this link: http://www.thermaltakeusa.com/product/power/purepower/w0120/w0120.asp

HD: WD 120 GB / WD1200JB-00GVA0
OS: XP SP2
Display card: NVIDIA GeForce 7600 GS AGP 8x
2 dvd/rw drives samsung/light-on

Okay here's my issue I built this PC about 9 months ago.
My original cpu was a Celeron D 351 3.20Ghz,
This pc was stable, never had a single crash or reboot,

Yesterday I installed a Pentium D 935 dual core Presler 3.2GHz.

My pc booted up fine, recognized the new cpu and loaded xp (sp2)
but....
I started getting random reboots and lockups. Sometimes within 2min other times a few hours..

After the first reboot I started using speedfan to watch the cpu temps, I never saw it above 41c, and I've tried other temp programs too.


So what could the reboots be from?
Would the CPU upgrade draw more power and make the PSU fail?

I used Prime95 and other stress test programs to heat things up, things ran fine (only tested for an hour)
Ram was tested with memt86 or whatever it's called?

I've used software like speedfan to watch everything,
Things looked perfect, temps, voltage, etc.

I even touched the CPU Heatsink after some of the crashes and it seemed normal, everything seem to be within it's normal temp range. I know what a cooked cpu feels like.
And I'm using the correct Bios
but I went ahead and tried all recent versions.

Maybe this CPU didn't like my slower dual channel ram?

 

[muz]

did you do a repair installation of windows xp ?
also i think a 500w should be ok but i aint to sure in that area
with this calculator i estimated you had a few system fans and other random stuff and it said 476watts so maybe you are cutting it a bit fine but wait for someone elses opinion on this .http://www.extreme.outervision.com/PSUEngine

 

[Raffaz]

You dont need to do a repair installation for a processor upgrade. I think its probably an installation problem and its overheating. Speedfan can sometimes report dodgy temperatures. Have you used thermal compound on the CPU etc.

Are you getting any BSODs? If its rebooting before you can see the STOP code, then goto system properties (windows key + pause break key) then click advanced tab > startup and recovery settings and uncheck the automatically restart option, this will stop it rebooting.