Volume control button not working

I have a Compaq Evo N800v laptop computer that's about a year old. The volume control feature has stopped working and the bar rests permanently at the bottom. I can slide it upwards but then it slides straight back down again.

I suspect that the cause may be that I spilt a bit of water on the keyboard yesterday. Everything was OK but after 30 mins or so the pc shut down automatically to protect my files and folders. After about 30 mins it started up again and everything has been working perfectly well except that I noticed that the volume is no longer working.

I wonder if some kind soul out there could possibly tell me how to cure the problem?

Cheers,
Sharon