Well I eventually got the hotswap rom trick to work, (thanks for the input), and now it works just fine until you change a bios setting. If for instance you change the core voltage from 1.65 to 1.70, save to cmos, it starts up again no problem and you can shut down (cold) and restart but if you use restart in windows or use the reset switch you get this on boot up before post:-

Award Bootblock bios v1.0

Bios rom checksum error

It's a new one on me. If you then switch off and on again it boots up fine until you restart or reset. If however you change the setting back 1.70 to 1.65 it will restart or reset just fine.

Don't you just love firmware