I'm building a new system (not the first I've built) using a new MB and Athlon XP3000 CPU. WIN XP Home edition on the hard drive from other system. I am also using other components from the old computer.

I installed everything and when I went to boot up it was only identified as a 1300mhz processor. I also got a floppy drive fail and shortly thereafter maybe 10 seconds the system shut down because of processor overheat. There is an LED for processor overheat on the new MB and it shuts down at 85 Celsius. I have the retail boxed set of processor/fan/heat sink.

A few minutes later I tried to restart it and I get no video signal.

I rechecked my work and I had the heat sink/fan on backwards. I reinstalled them the correct direction and I still get no video signal. Cable and cords are good. Monitor is good and the monitor shows there is no signal coming in when I unplug the monitor from the video card.

Tell me I didn't just fry my processor!

The cpu reading is probably due to the fact that the FSB on the mobo is set to 133 or even 100 as default. That can be changed, but let's hope your cpu aint fried. If your system shut down as soon as the processor hit 85c, then I would like to think that it's a saftey measure to avoid physical damage.

I've never seen a damaged cpu, take off the HSF and get a close look at the processor. Does it appear to be damaged?

List your other specs: mobo, vid card, ram

Indeed. i hope it didn't already fried.

Take out Video Card, see if there is any dust in the slot (clean it). Put it back.
Clean the CMOS in order to reset BIOS settings. For that you have to take out the CMOS battery, count slow to 10 and put it back, sometimes you also have to move jumpers (for details check mobo's manual). Then, in BIOS, set the FSB to 166Mhz, multipier 13x (though it may be locked and don't need changes). Does if fix your prob?