Beeps and Errors : (

I decided to replace the heatsink on my old athlon which is in an A7V133-C motherboard, the problem now is that when I turn the computer on it posts fine, and brings up some stuff to do with the network card (booting from the network) and sometimes reaches the windows loading screen, but then beeps three times and all the fans on the motherboard stop and the screen goes blank, while the case and PSU fans still go, I read in the motherboard manual that one beep (at post?), then three beeps meant that the video card couldnt be detected or the video memory was screwed, which I thought was a bit suspicious as I had only just put a new heatsink on my graphics card ( a Geforce 2 GTS), however it had booted fine before with the mod on the gfx card. I also tested a Voodoo 3 2000, which I also know works, but again I got the same beeps... : /
Im thinking that this is a motherboard error as opposed to windows as the beeps are represented in the manual, but as I have only changed the heatsink on the chip (to a better one) then I really cant see why it would do it.

The motherboard manual also had information on other system problems through beeps, it said that high pitched beeps that keep going means that the CPU temperature is too high, but the computer was running slower than spec anyway (its a 1.4GHz Athlon, I was running it at 1.1GHz)

Ideas anyone? Any help would be appreciated.

Two words: Heatsink contact. T-Birds are hot chips at any speed, and if the computer is crashing after post, that means something is becoming unstable. Reseat your heatsink, and check to see if you either didn't use enough thermal grease or too much.