Finding an Electrical -- Break? Open? -- Caused by a Rodent
I'm not a pro, but I'd be doing continuity testing. With a multimeter or other such tool and a few lengths of stranded wire, I'd test each conductor (black, white, bare ground) between known points on the same circuit. Once you have that you can trace it or run new wires. 

You'll want a non-contact voltage tester to be safe.