Bad processor - no video

Problem is solved, but i still want some info.
So if you are CPU savy or can provide me a useful link. (Google doesn't like my search terms)
Recently i changed out my Athlon 1800 for a 2200. PC booted and worked fine, but my
temperature sensors showed CPU at 150F at idle. It would easily hit 170 while compiling
or burning a disk. So... i figured the heatsink/fan was too small for the new CPU.
Looking through some old donor boxes i found one with a thermaltake heatsink/fan. At almost
double the size of the original i figured this would help cool better.
After a quick swap i booted up and had no video signal. At first i just thought it was a glitch, i have
a monitor on my test bench that exhibits the same "no video signal" behavior on some machines.
Unplugging it for a few seconds fixes it. I unplug the main monitor, wait, and plug it in. Boot the PC
and get no video, although i can see the HD light and can hear the drives spin up.
Troubleshooting goes: swap monitor, swap video card, put video card in different box (it works),
decide the AGP slot has gone bad (from changing a heatsink/fan) and clear the CMOS. Nada!
Stop by local shop and grab a PCI video card, it fails. Test it in good machine, it works.
Back to Google and have two suggestions: MotherBoard or CPU. Not excited about changing out
the MOBO i swap the Athlon out with a Duron i have in the donor box.
Boot up, lights flash, drives spin, monitor comes on...wo0ho0!
Now i know this is a long read for this simple question: How in heck does a proceesor go bad
in such a way that the machine still boots and only the video is affected? Keep in mind this box
has an AGP slot and no on-board video.

You likely chipped the core swapping out heatsinks.

Thank You. I now realize I might be an idiot.
After your post I grabbed the CPU and got a magnifying glass out.
After cleaning off the thermal paste I examined it like a CSI agent.
No chips, scratches or other indications of defect.
Purely by accident I flipped it over on the pin side...

Edited by raw, 01 January 2009 - 06:54 PM.

Had to use PhotoImpact to see those defects/scratches...that smudge looks like something besides dinner has been cooking (possibly).

I've had bent pins before, had to take it to shop and let someone else tell me they were bent...I never would have arrived at that knowledge on my own .

Louis

Actually the "scratch" is a line trace. Dinner cooking would be closer
to the burn mark.
From the first post: This CPU has run hot since day one - 150F at boot, 160 just browsing/surfing
and 170 under load, but it always worked.
I never looked at the pin side so never noticed the burn.
FYI - double check the the heatsink...AMD's will fry in under 1 second.
Just strange to me that this only affected the video signal.
The replacement Duron has not exceeded 120F yet.