MBP LCD screen suddenly not working after power issue
A couple of days ago, I had my 2012 MBP (MD101LL/A) closed and in sleep mode - when I opened it, nothing happened. There was no power (battery indicator didn't light up) and wouldn't do anything even with a power cord attached. I opened it up and disconnected/reconnected the battery and then the MBP would turn on, but the LCD wouldn't show anything at all. (When I had it open, I had disconnected/reconnected the LCD data cable as well. When I did that, I pulled UP which I realized I shouldn't do, then pulled ALONG the logic board) Thinking I reconnected the LCD cable incorrectly, I went back in and reconnected it, but it didn't help. I then reset the PRAM and SMC thinking that would help, but same black screen. A connected thunderbolt display works perfectly fine.
Any ideas as to what can be the cause? I don't know if I should be looking at replacing the whole LCD or just the data cable or if it could be something bigger and more expensive. My guess is that when I pulled UP on the cable, it did something, but I wanted to check with you guys before I did anything.
Can I bring this to an Apple store to have it looked at? I had bought it off ebay where the seller had installed an SSD and some RAM, then I replaced the DVD drive with a HDD. Not sure if they would diagnosis it if that work had been done.