Might be getting somewhere thanks to you guys :)
I unplugged the HDD and FDD from MB , left the DVD rom plugged in and powered up
the box.
I got a single beep (no beeps previously), keyboard led's blinked this time and
the monitor sprang to life :)
It could not boot without an operating system so I shut it down and rebooted
this time with my Ubuntu 7.10 live CD in the DVD rom.
I did a memory check using Ubuntu in live mode and so I figure that the
motherboard isn't totally fried if it will do this much.
I have a couple of spare hard drives here so I will swap a good one in and see
if that fixes the problem.