Well,you've done a great job researching possible solutions and assuming you applied them properly, everything points towards a logic board issue. You could have damaged the charging circuit, which would impede the startup of the device or you could have nicked or dislodged some components. About the only thing you haven't tried is to inspect the board under magnification to see if there's anything obvious.
At this point, your best bet is to have it looked at by an experienced micro-solderer.