Back cover makes MBP unresponsive

I just changed my Superdrive out with at MCE optibay with an SSD and changed my system disk to run on the SSD. also i upgraded the RAM from 4-8 GB.

The problem is that when the back plate is on the computer becomes totally unresponsive. It works great when the cover is not on but as soon as it comes on the screen begins to flicker and the mouse and keyboard does not function. All i can do is to shut down the computer by holding the power button and when it starts up again nothing happens. sometimes if i put the cover on really carefully its all right but then when the last screws come on it goes haywire. It seems that something is pressing against something it shouldn't but i can't figure out what. '

Please help