Thanks Richard, excellent advice (as always).
Stripped it down as you suggested and it ran fine.
Mouse and keyboard working fine.
Then I reattached the second CD drive and the USB internet wireless adaptor. Still no problems
That also rules out a pest.
It MUST be the soundcard. I will reattach it and install the latest drivers, and see if it works.
If not, I will buy a new one, any suggestions?