My iphone power button had worn out and had become very stiff to press so I took it apart, and identified the power button was missing the black nub. So I ordered a new power and proximity sensor cable.

I followed the guide on Ifixit to replace the cable and put the phone back together carefully making sure all the cables were in correctly. I tried turning on the phone and there was no power at all, even with the charger in.

I tried charging the phone for a few hours and still got nothing. I then took the phone apart again and looked at the cables at the top, as soon as I unplugged the new proximity sensor cable the phone randomly powered up and worked fine apart from the sleep/wake button and proximity sensor. Every time I plug the proximity cable in I get nothing the phone will not turn on but as soon as I unplug it the phone powers up every time.

Does anyone have any ideas what is wrong?