macbook fan won't stop

This started happening after I played a network game of that big-bang-board-game chess program that comes on all the new apple computers. Ever since then my fan has run a lot and won't stop. Even after I leave the computer off for a while to let it cool down and start it up again.

It never used to run this loud, nor for this long.

The good thing is that the computer doesn't seem to be over heating... I just don't want my poor macbook to run it's fan out when it doesn't have to

Any ideas?

Thanks.