My laptop fan stopped working after installing Linux. How do I fix it?

I installed it a a few weeks ago. I used to have windows vista and changed to UNIX Ubuntu 8.04, which is what I hold now. I have been having to keep a REAL fan on top of the bottom of it to keep it from overheating and shutting off. Its hence annoying. I thought that possibly its missing driver but I really have no clue. any help???