Lost power

[85 250sx]

well as of 2 days ago i lost all power in my shed. I have tried different things but i still cant find the problem. It has its own circut breaker and ive tried turning it on and off but that didnt work so i changed the 3 fuses but still no power. we built a garage here over the summer and ran into the power wire that goes to the shed. now im thinking some one may have nicked the wire and it just now may have broken apart? are there any devices that i can buy to check and see where i stop losing power? like without having to strip the wire in 20 diffferent places?

[85 250sx]

ah come on no electritians in here? id like to try to fix this soon. im having to run an extention cord from the house and it sucks cause i can only use one tool or light at at time. if i run a tool with the lights on, the lights go out for a sec. and if im using the air compressor the lights dont come back on till the compressor turns off. and i cant un plug the deep freezer either! lol