iPhone wont turn on after screen replace but vibrating

Hello, recently my mate brought me his iphone 6 which after replacing screen in no named mobile fix store with unsticked screen from the frame that I was able to see inside the phone throught this “unsticky screen”. I told him that is not big problem, i can put adhesive there and stick it in. So i did it, I opened the phone, uplugg battery then screen, put adhesive under screen and then made everything together. Everything was good, so far, and then after approx 20 minutes screen lags, pixelate and go black and not turning on. I thought that can be some mess on connector because phone was messed up inside from that hole. I tried put in charger, put to itunes and tried to turn it on but nothing worked. So i opened the phone, tried just unplug and plug screen and then it worked some how. I said myself that i will disassembly and clean it all with soft plasic brush. So i did, connected it together again and what, I cant boot it up, not respond anything, sometimes if i am in random time pushing buttons for hard reset it just vibrate but nothing more. No itunes respond, just heating up in charger. Have someone idea what can be the problem please ? And yes firstly i unlugged battery then screen. Ps. Another battery nothing changed. Thanx <3