|ALWAYS unplug the computer or otherwise switch off the AC power to the computer whenever you're fiddling with plugging in or unplugging wiring or components inside the computer case.|
The wiring connectors from the power supply will plug into only one type of power socket or connector.
The 20 or 24 pin main connector from the power supply must be plugged into the 20 or 24 pin main power socket on the mboard. If the socket is 24 pin, the wiring from the PS usually has a 20 pin connector with a 4 pin connector in the same wiring bundle that plugs in beside the 20 pin one - they can only be plugged in in the proper places. On most modern mboards there is also a 4 or 8 pin power socket on the mboard a connector from the PS must be plugged into.
If you have a video card installed in a mboard slot, it may have one or two power sockets on it that a connector from the PS must be plugged into.
The 4 pin molex power connectors, or the SATA power connectors if that applies, from the power supply must be plugged into the drives.
The data cables must be installed between the mboard data headers and the drives.
The female wiring connectors from the case must be plugged into the proper headers for the front panel (Power switch, power and hdd drive leds) and USB.