why does the phone work with a black screen?

[Android Central Question]

so my phone worked before it fell and it started of as only the bottom screen black but the day after that it turn all black but the phone still rang and i could still answer and talk so i went to fix the lcd repair nd they gve me my phone but now they told me it turns off and on by itself all the time so i cant do anything what is the issue?

 

[belodion]

My word, that would be difficult to diagnose via a forum. A faulty power switch? Damage done to something during the repair? A bad battery or battery connection? Something else?