It might be a memory problem also if your new CPU has a higher FSB.
Try reseating all your memory sticks and if that doesnt help, try picking them away one at a time to find the bad one.
"One thing we did run into on the KT7 was the fact that if you populated all three DIMM slots, it led to some board instability using Win2K. However, this problem continued even when only two slots were populated. It was suggested to us by an engineer that we use slots 1 and 3 when using two DIMMs. This is not a solution that has been tested by us, but we wanted to pass the info along. The Southbridge used here is the 686B, which means that ATA100 support is native on board. Also, you can see that the ATX power header is tucked off to the side and out of the way. Also worth mentioning is a new safety feature that ABIT is putting in some of their BIOSes. Just as many have learned, the AMD CPUs are very fragile when it comes to heat and handling. Now on some of their BIOSes, if you do NOT have a working fan plugged into the CPU1 3-pin header, the board will not boot. The CPU1 fan header is the one closest to the DIMM slots. "
Ouch.. 686B chipset.. This might well be the heart of your problem. I had exactly similar problems with the KT7A-Raid which forced me to change it to a KT266A board.