Unhappy [Q] Tried to make two tablets out of one, got vertical lines on the screen

So I dropped my nexus 7 and cracked the screen. My friend dropped his in water and it wouldn't turn on. So I bought his wreckage and put his screen (LCD + Digitizer assembly) on my tablet, and this is what I got:

Display with vertical lines

I tried disconnecting and reconnecting the screen, and it's the same. Any suggestions on what could be the cause?

Thanks in advance!