KT7 MAX2 Problem

[BT News]

I have the above board with a 1800+XP athlon. I'm running Win XP Pro. can't get system to boot when the cpu is configed as a 1800xp. system just wont boot. getes to the win xp splash screen and then just restarts over and over again. will only run with the cpu stated as a 1.15GHz. Updated(flashed) and reset the bios but still had no joy. Any1 got any idea. Have been told it cud be a dodgy CPU. Have tried everything and had no joy, some advice would be much appreciated