I think the CPU is OK Richard, I know +90C is dangerously high but it's still working.
I suspect the problem has been overheating all along. I've ordered a new cooler which is good for AMD athlon up to XP3400Mhz.
Before, there was no thermal grease on the CPU, just the pad on the bottom that came with the cooler.
Yesterday I added Antec thermal grease and it cooled it down significantly but the CPU still runs up to well over 70C.
It was booting at 78C before I added the grease, which is far too high which suggests a cooling problem.
How do I know if I've cooked the CPU? Would it work at all?
Cheers