Is your computer OEM (prebuilt) by a big company like Dell/Gateway/HP, or was it made by a local computer store?
If it was made by Dell/GW2K/HP, it is probably a proprietary power supply of some sort (i.e., Dell has auxillary connectors). If it was made locally or by a small company, it could be anything. Best bet is to open your case, uplug the power supply from the back, unplug the molex 4-pin connectors from everything, disconnect the big 20-pin connector the the motherboard, and unscrew it from the back. Look at the markings on it, write them down, and post here. Then screw it back in and reconnect everything - the molex connectors only go on one way so you can't mix up the +5v and +12v leads, so there's really minimal risk.