Introduction
1* Take the battery out.
2*Unscrew the whole back.
3*You will see a connector down at the charger port take them off and you can blow some air to take the dirt off.
4* Take some paper and fold it 4 to 6 times(small one)
5* After folding it make sure it is the size of the connector that is next to the Camera.
6*Place the folden paper on top of the connector.
7*Slowly get back all the plastic covers.
8*Screw in all the screws.
9*Place the battery, SD Card and the Sim back
10*Power on the Phone.
99.9% It will work.
UPDATE:
If you want to take it a step further,
get some thermal paste
and remove the whole circuit board and put some on the spot (as shown in the picture) do NOT put too much a dot will be enough...
after that, you can go ahead and place the circuit board back in place, then place the paper on the connector(follow the steps 6-10)
*Even thermal pad might do the job.
Thanks,
I hope this will fix the problem !