Start up fault

Dell 5100
Win XP

When I swith on the UPS, the PC starts by itself.

Then goes into 'Performing automatic IDE configuration...' and I have to hit F2 to reset the date & time.

Off/On button or control relay fault?
DC power supply fault?
Motherboard fault?

Any ideas or tips would be appreciated, thanks in advance.
I'll admit im not a great PC person, but if its not storing the time/date maybe its just the motherboard battery (yes there is one on it!) is flat..

CMOS battery needs replacing. Looks like a small silver disk on the motherboard, usually no more than a couple of quid.
Thanks and you're correct, it's the duff battery that won't allow date memory.

Just that I can't understand the computer starting up by itself as soon as the external UPS supplies power.

Thanks for your help so far anyway folks, much appreciated.