Changed Screen and now iPhone won't turn on and iTunes won't recognise

Changed my phone screen today as i was assembling it the screen was on but had rectangular shapes at top of screen so i took it apart then back together and it was fine, as i put the screws in for the shield the phone went off, the apple logo then showed and then blank again. phone was dead for ages tried everything. anyway put it back together and left it on charge and somehow after around 45 mins it came on randomly at 61%. It then worked fine for about 30 mins before turning off again and is now dead. Any ideas? I'm thinking either Long screw damage or bigger fault, i just want it back on long enough to back it up or even work fine again. Thanks