computer getting very hot

I just purchased a dell latitude second hand. After it has been on for 10 - 15 minututes it starts to heat up and gets hotter and hotter - the heat seems to be comming from the right up side of the key board as well as the right side of the screen - IS THIS NORMAL??? the fan does not seem to be working?? but maybe I have not left it on long enough for it to kick in. PLEASE HELP!!!!