Well, I took no chances and refitted my processor with fresh paste.
Interestingly, the temp shown in the BIOS is set at 55 deg and the fan is maintaining that.
Diagnosing this BSOD is becoming a nightmare as now it will not boot from the hard disc at all. Gets to the options page (Safe Mode, Safe Mode with Network, Normal etc) but will not boot from any selection, it just goes into a loop and returns to the same page again. It will boot from the setup disc to the install/repair diagnostic but it can not automatically fix the fault, gives an "error during setup" in the fault details list.
I can't disconnect the video card as that is the only means of connecting to a monitor/tv. I thought I had a VGA socket on the mobo but it turns out it's a DE-9 not a DA-15. (All my monitors/tvs have VGA DA-15)
So, it's either off to the repair shop or start purchasing hardware to swap in and out.
Much of the stuff on t'internet suggests conflicts between the video card/driver and onboard sound but my system has run for the best part of 2 & 1/2 years without major problems so why would it just fail now?
One 'fix' touted around the net is to disable C1E in the BIOS.
Another is to jump the CMOS. A complex manouvre involving turning the pc off moving a jumper, pressing the on switch with power off.........zzzzzzz
I personally suspect the hard drive, but that is just a hunch.