Assuming that these are rated at 12VDC (most are), you need to "steal" 12VDC from one of the HDD power connectors. Hopefully you have an ampty connector, and you can find a male one to plug into the jack. If there is no empty connector around, you may splice the GND and 12V wires from a used one. This requires a small amount of electricianship, and you could get it done by any computer repair shop for a small fee.