Suspect list: Though it is slightly possible that a dirty 120 volt plug is the problem.. And I would clean it if it needs cleaning (I do this often on my 30 amp cord) I doubt that is your problem.
Suspect list:
#1: Tripped branch breaker
#2: 12 volt issue, starting with dead battery
#3: Blown fuse, bad disconnet or bad connetion INCLUDING THE GROUND (12 volt).
#4: Deceased air conditioner.. (Alas Murphy rates this #1 since it is the most expensive item on my list).
FACT: In this lovely warmth we have here in Southern GA. one of my units has taken to tripping it's branch breaker. Now in my case I know why it does this and I can work around it.. (For reasons I understand it will cycle even if room is still too hot.. When it restarts it clicks the breaker off). Thankfully there is an alternate mode where it does not cycle off till I do it manually.