Fans stop when os starts


Jan 28, 2010
Hello, I do know if I am posting the right catagory

I have a older compaq presaio 64computer
model 6430nx
serial MX30307033
with a amd 2600+ processor

The problem Iam having is When I first boot up the computer
The exaust fan and cpu fan are running good
but as soon as the os ( xo pro with sp3) boot up the exaust fan
stops and the cpu fan slows downs the computer then begins to keep restarting after it get s hot or iam running a a scan so I had to open up the side and have a small fan blow in
I have reset the bios to its default state other then the fans stopping that appears to be the only problem with it

What should I check for
besides Bios

Some one said it may be my power supply but I do not feel that is the problem as the fans are going good and strong untill the os boots up

What should I check for
besides Bios