iPhone Power button Issue and Battery Issue.

Bought an Iphone to repair.

I replaced the screen and in doing so ripped a ribon cable. therefore I bought a new cable. 9the cable being power button, ear piece etc.

On installing the power button does not work, what could be the problem? is there a special way to put it in.

Also the battery used to die at 50% ish?

What is the cause?

It has now gone down to 2% since last night, so hope it was just an error which has fixed itself.