Stupid computer!

I have just reformatted and reinstalled Windows after running Linux. Now my computer is constantly freezing up. The only way to get it going again is to push restart. After this the first screen on boot gives the messages 'Suggested DRAM CAS latency is '3'' & 'suggested DRAM clock is '66''. After that it dies half way through loading and says 'HIMEM.SYS has detected unreliable XMS memory at xxxxxxxxx address' (address changes). then it displays 'XMS driver not installed HIMEM.SYS is missing'. Sometimes it says that there is insufficient memory to load Windows and shuts down. The only way out is to turn it off then on. Memory chips are properly seated, Norton Utilities test says memory is fine, and motherboard monitor shows no spikes in power or temp (what is safe temp for CPU?). Could this be a software problem? It seems that the RAM could be bad, but it was fine before reinstalling Windows.
Computer is a P3500 with 128MB RAM.

Do you think maybe bashing it flat with a sledgehammer would help?!

Thanks.