You will not need a heat gun to disassemble the base part but after unscrewing its screws, you need to have something really thin to detach clips and also to ensure you will not hurt the phone... it holds together really tight also without screws...
Anyway, I have heard USB board itself may cause such behaviour, so it may happen you will only need a replacement USB board.
Also, if you disassemble your phone, you may check its connectors (basically under a metal part which helps these connectors to remain in place).
If they are connected well, I would also try to switch the phone on