If you want the SSD to power up and function, it needs to be connected. What make and model of power supply do you have? Note that sata power cables usually have 2 to 3 connectors along it's length. You can plug in multiple devices into this one sata power cable. For instance, look at the sata power cable attached to your HDD. There's probably another connector on the cable to connect to the SSD (as long as it reaches).