Lappy-Right-click context menu keeps popping up all the time!

Hi all

I've got an HP/Compaq Presario 2500 laptop and as the title says, the
Right-click context menu keeps popping up all the time.....but it's
intermittent, sometimes I can switch it on and it might take 30-40mins to
start happening, another time it'll happen almost straight after boot up,
sometimes not at all till next session!!!

I've run virus checks and spyware tests - all negative. Even if I turn off
the touch pad and use a USB mouse - it still happens!!!

It's not a driver issue either - I re-installed XP and it started playing
up when I came to input the regional settings.

It's driving me nuts!!!

Any educated guesses? Could it possibly be a faulty battery or contact?
I've had the lappy seem 'dead' a few times over the last few weeks when
pressing the 'Power-On' button and have had to pull the battery and re-
insert it to get the machine to power up!!

Regards and thanks in advance for any ideas you can throw my way...
.