Latest update, if anyone's still watching....
Did the following, but not necessarily in this order:
Disconnected then reconnected the CMOS battery.
Removed all the memory (four sticks of 1GB each)
Replaced stick in slot 1 (actually, swapped it out first)
Rebooted
Got to the familiar 'problem' screen
Reflashed the BIOS
Rebooted...and hey, got to the BIOS screen (but not Windows)
Tried to run Windows in Safe Mode, but system just switched off
Did this several times
Got into the BIOS and fiddled about with some settings
Got into Windows!
Rebooted OK
Added more memory, rebooted.
Did this till all 4 sticks were in.
At some point the BIOS crashed again and I got thoroughly ****ed off and decided to leave it for a few days.
Removed the battery again
Removed all but one mem stick.
Rebooted & reflashed BIOS
Rebooted into BIOS and made a few random tweaks
Into Windows OK again
Restarted several times and so far OK...but...
am concerned that all might go pear-shaped again. However, will see how it goes for a few days then slowly reintroduce the other memory sticks. Someone mentioned that the memory might be a problem, so we'll see.
Any other suggestions as to why this problem may have occurred and what I can do to prevent it happenning again? Presumably, my mobo's OK? Cheers