Overheating motherboard No Display and Computer wont recognize

Hey guys, I appreciate all you do and thanks for taking the time to read.

I have two iPhone 4S motherboards that wont boot, or be recognized by any computer, But they do start to heat up once plugged into the computer or power source. The section of the MoBo that heats up is just above where the charger port flex cable plugs in (I believe its the heatsink fan-ish area) heats up slowly but very noticeably hot.

History- the first iphone 4s was slammed against the corner or a desk bent to heck. After i replaced the display the device turned on and worked perfectly....

To try and save a few bucks I disassembled all the parts, carefully taped down the flex ribbon that's adhered to the bezel, wrapped in 1 layer of bubble wrap and used a rubber mallet along the edge of the frame to straighten it out.

Checked all cables for damage then re-assembled iphone and...... Nothing. Just heat, no display nor will any computer detect it

I even went as far as to switch motherboards with another 4s that was working perfectly, once i traded MoBo's.... Nothing.

So i dont think i caused any damage to the flex cables during my highly technical and complicated procedure of hammering the frame with a mallet.... lol

Any Ideas guys???????