Why is my screen staying black?

[M-a Richard]

I have a samsung galaxy S3 and a while back a purple spot appeared at the bottom and expanded until my screen became all purple and eventually just black. I though that it was the digitizer that messed up or i broke the lcd screen so I ordered one in and it finally came in today. Now Ive just finished changing the screens and hooking everything up again, but my screen still remains black, Ive also tried scrubbing with rubbing alcohol the connector pins between the motherboard and digitizer and it still didn't do any good. Anyone have an idea whats actually causing this screen glitch on my phone? Thanks in advance!

And yes all the other buttons still work fine and I can turn on my phone, but I cant get into android recovery or factory reset or anything, please help if you can!