Circuit rewired to accept 5th receptacle
If the the AC power wires are connected to the receptacle using poke-in type connections then it is the possible source of your problem. 

The string of receptacles are wired in a string. The AC feed starts at one end and feeds the first. Then another run of wire daisy chains to the second receptacle. This repeats to the last one in the string. 

If you are using the poke in style terminations for the wires do know that the poke in lock mechanism inside the receptacle is fabricated out of the same piece of metal as that which engages the ends that you inserted into the outlet. If you had difficulty pulling out a plug it may have deformed the metal contact in such way that the poke-in lock on one of the wires has disengaged the wire and is not longer making a connection. All the downstream outlets that depended upon that wire will no longer be powered.

It is also possible that the hard to remove plug caused an improperly installed poke-in wire to slip out with just the flex of the contact as you tried removing the plug.

If this is the likely description of your problem it may be necessary to replace the problem outlet. 

Many here also consider the poke-in style of wire terminations on outlets and switches to be crap. It is far better to use the screws supplied on the side of outlets to connect the wires.