A crossover is made where the two sections of the home go together. The electrical cross over is just a junction box where the wires connect. It could be in the end wall, under the floor, or in a closet, with an access panal. An inspection will reveal its location. This may be your problem, but it can also be an individual circuit, ie, receptacles are wired one to another, if the "feed thru" on the last working receptacle is burnt, or otherwise disabled, that receptacle will still function, but will not allow those down the line to function.