|".....however the drives trays will not open..."|
Optical drives require 5v, as does your floppy drive and some other components includung USB.
If your optical drive trays don't move, it's quite likely your floppy drive and USB ports don't properly work either.
The drive trays moving in or out when you press the button on the front of them only requires they be connected to a properly working PS and the computer is running - the data cable does not have to be connected, and they should do that even if the mboard isn't working properly.
Your PS is probably either.....
- putting no +5v at all, or putting out +5v but it's actual value is too low.
- OR - the actual voltage that is supposed to be +5v may be way too high - that can fry the PCBs on optical drives and floppy drives in a short time. Their leds may still come on, but they don't work properly otherwise.
I've seen cases where a PS is putting out no +5v at all, yet the hard drive and mboard still work fine, aside from the USB ports if applicable.
Your fans use +12v but they are much more tolerant of the actual voltage being too low or too high.
Failing power supplies are common and can cause your symptoms.
Check your PS.
See response 4 in this:
They often still partially work, yet they won't allow the computer to boot all the way.