Try connecting it to a different power connector. If that doesn't work, try removing the data connection and having it just plugged into the power connection. Then try opening it. If it opens then, there's something wrong with the motherboard or possibly CPU.
The thing is, the CD-ROM has its own controller for opening and closing, but when the data cable is connected, opening and closing of the drive is taken over by the processor. This way, software can open and close the drive, or a program that's installing can tell the processor to keep the drive shut until it's done, et cetera. So, put simply, if it opens when the data cable is not connected, there's something wrong with the motherboard/CPU. If it doesn't open even without the data cable, the drive probably went bad.