Computer randomly hangs or freezes

My computer randomly hangs or freezes. It happens in any program or even while idle on the desktop. Before it hangs it always makes a little clicking sound from in the case and I have not been quick enough to see where it comes from.

Computer system:
Dell 933 P3
Windows 2000 prof
256 ram
Dvd
Cd burner
250mb internal zip
ATI radeon ddr 32 mb video
Direcway 2-way satellite modems
all updated drivers including SR-2 (windows 2000)

Actually the problem didnt really start to surface until after install the satellite modems(USB) No help from Direcway.

Event viewer does not show anything right before lock-up. Any help? I don't know where to start. I can not contact Dell because the computer originally came with Windows ME.
Thank you!!

 

I had problems with drivers for several brands of analog USB modems. Try removing and see if that stops it.