BleepingComputer.com: Troubleshooting Motherboard

I have a couple of computers I was given (4) from a friends office that dont work and have seen different testing tools for the motherboard and was wondering how and what everyone else uses to test the motherboard in terms of these testing tools..some are usb and others clip into the motherboard itself with a digital readout..The other components of the computer I know how to test...thank you