Get ready for some detailed feedback. Whoever solves this gets a prize.
Sourced a new board. A Biostar A780L BS710.
The other components remain the same.
Took it to IC (i know but don't judge, the guy did not even charge me). He connected the PSU. Plugged it in. It posted fine with no hdd and with the new blank 1TB sata drive i had bought from IC a few weeks back it also posted fine.
Brought it home. Did the same. All is fine. Boots and posts fine. Get to the end of the intro to the windows xp install process and it says it cannot detect any hdds and has to quit.
Try my original 80GB sata hdd with xp already loaded on it. Using the same sata cable and power cable. No other peripherals. Just keyboard and mouse.
Pc does not boot. Lights come on and all fans spin up for a split second then it goes dead.
Try the old 20GB IDE hdd from my P3 which works in my P3 just fine. Even remove the IDE cd drive and set the hdd to master and to first boot device in the BIOS. Pc boots. Gets to that recovery screen saying "windows did not shut down properly" etc etc. Whichever option i choose it just restarts and i end up back at that screen...and again and again...
At one stage i got very similar errors to the checksums i was getting with the old board saying that CMOS settings are wrong and to set the time etc. They seem to have gone now that i have set the time in the BIOS though it might have been when i took out one of the RAM sticks. In any event that message has disappeared as i stands.
Have tried all four of my RAM modules. Tried using the onboard video. Tried with GPU. Tried without. Tried a different power cable to the PSU(which i just bought let us not forget).
Does this leave the CPU?? I cannot think of anything else. And i cannot fathom why my initial hdd being plugged in would cause the pc not even to start at all.
Wits end reached.
Prize to anyone with a solution that does not involve either lugging the machine somewhere again or replacing the cpu and/or RAM.