Deskpro 4000 without fans

Hello!

I have a Deskpro 4000 (rather old, Pentium 166MMX, 128 MB) which I use
as a file server and firewall. It works quite find, the only thing
disturbing me were the fans. I replaced the CPU-fan successfully with a
passive cooler and I use a very, very silent Seagate harddrive. The only
noise producing component now is the fan of the power supply. I really
don´t think that it is necessary cause it moves only cold air out of the
power supply. I tried to cut one of the cables of the fan but then the
Compaq cannot be powered on. Maybe there is a built-in means of
protection. Does anybody know how to fake the mainboard to start without
a running fan?

Andreas