Is it around the edges and have you wiped it with wet wipes?
I made the mistake of wiping mine with a baby wipe a while ago (yes i know its a silly thing to have done) and where i had done round the edge caused liquid to seep into the screen and that made it look like a big bright spot on one side of the screen but it slowly faded as it dried and was back to normal after a couple of weeks could it be that?
If it is pixel sized though it could be a stuck pixel which can some times be fixed
http://www.geeksaresexy.net/2007/08/...an-lcd-screen/