Power to dead circuit
In the panel just pull the wire off the dead breaker and put it on a breaker of the same ampacity that is working.   

If there is already a wire on that breaker, check if the breaker is listed to accept 2 wires (a few are, e.g. pushmatic).  If not, then pull both wires off the breaker, wire-nut them to a 6" pigtail, and attach the loose end of the pigtail to the breaker.  



The other option, not quite legal, is to get a power cord of same gauge as the circuit. A power cord can be obtained by chopping the socket end off an extension cord.  Have the bare-wire end of the cord enter the panel via a properly sized strain relief.  Pull the hot off the defective breaker and its partner neutral (must do both). Nut them to the hot and neutral of the power cord.  Then plug the power cord into any working receptacle.


Now, why use a flexible cord and not Romex? It's illegal to use Romex for line cord.  And it is illegal to put a plug on Solid wire cable. 
Why make the Romex-cord splice inside the service panel?  Because it has to be inside some sort of junction box, gutter or panel, any would do, just the circuit already goes to the panel.
Why neutral too? Imbalance of currents / eddy current heating / other badness.  Always have the return current (neutral) in the same cable or conduit as the hot(s).