No power (Compaq EVO D310DT)

Question

Computer was working fine and pleeping at me every now and again!!! Went to use the computer and it had no power (as normaly leave it running) and would not power up with no lights on at all. Tried unplugging the power cord and pressing the on button whilst plugging the cord back in and the lights flash then die out!!!!!Think it might be the system boards battery (3v)Could anyone help cos i'm pi**ed off with computers now!!Regards