Having booted the NAS and had it running for some hours performing backups, I put it into shutdown.
After what seemed a little longer than normal it did complete the shutdown and power off, never to power up again...!
Now the boot screen comes up but the rest of the POST fails to happen, re-seated the memory and connectors but still the same, oh well off the eBay for a new secondhand MB
Sticking with the 775 CPU and DDR2 format so I can use these off the failed board, just hope they weren't the reason for the failure..!
This time I've gone for an Intel mini ATX format, no real reason why, just don't need the expansion sockets of a micro ATX. With three sata ports it gives me a spare port for when I add to the current single 4TB drive.