Screen intermittently works, sometimes black

My Nexus 5 screen went black the other day, the backlight is on and the phone works but I just get a black screen. I tapped it on the back and the screen came back but then the digitiser didn't work. Tapped it again and then it worked perfectly but half an hour later black screen again.

Ordered a replacement screen but the same thing happens, I noticed that if i tap the motherboard this temporarily fixes it giving me the impression that there is something wrong with it.

I've checked ribbon cables and connections many times but no luck.

Any help?