Phew. It is an old AT/LPX standard, you cannot use an ATX power supply with it directly, unless you get an adapter from 24 pin ATX to 12 pin AT (it is not 14 pin, mind you). Either that, or you will need to get a replacement PSU from the original manufacturer by contacting support. That's one of the reasons pre-built systems can be a headache. Many strange design decisions.