I've never had a laptop apart so consider that when reading my post.
Let's start with when any electric connection need to be shorted something has gone wrong . Where ever exactly you are shorting the circuit it is obviously no longer completing this circuit in the normal manor. The short doesn't do it correctly either because everything doesn't come on.
The on switch that you are using may have more than one terminal that supplies power to a different location on the MB . So it is necessary for the power to leave both locations & the one "short" doesn't do this. There may be a "switch" on the MB that the on switch activates . That may also distribute "power" to more than one location .
I would try to find a manual for your computer.
Do the procedure for resetting the eeprom or cmos .
try that & maybe take the MB battery out if it has one.
Maybe the manual will have how long to keep the battery out.
If not at least an hour & maybe a day or two.