Laptop freezes with FC5

[Andrew Robinson]

I have recently installed FC5 along side of FC4 on my emachines laptop. 
When booted into FC5, after running for a period of time, the laptop 
suffers a hard freeze. No keys work. The mouse does not work. I cannot 
ping the laptop from other PCs on my network. The only way to regain 
control is to hold down the power button until the laptop powers off.

I strongly suspect this a heat issue. The friend I got the laptop from 
originally bought it at a deep discount because it would freeze up on 
several prior potential customers. He realized the fan was not running 
after the laptop booted and concluded that the WinXP home edition 
installed did not have a driver for the fan. He loaded Ubuntu and it 
worked like a charm. I have been running FC4 for 4 or 5 months without 
problem as well.  The problem has apparently returned with FC5.

Anyone know what I need to do to get FC5 to run the fan on my laptop? 
This is an area I am very ignorant in.

Thanks!

Andrew Robinson