OK, update:
I purchased a new cable, installed it, and things were working ok.... for a short time before I got the same fault :-(
I then tried a different power cable - no difference
I then tried a different BIOS setting or two - no difference
About the only thing that I can think of that I haven't tried is another PSU. The current one is a 200W model, running a P200MMX, 1xHD (4GB?) 1xCDROM and about 4xPCI cards, oh and the mobo ;-)
Is it possbile that there is not enough power? I could try removing the CDROM (would be the easiest, cos I don't fancy mucking about with all the PCI cards!)
Any opinions? :-)
Cheers
Rassilon