Guitar problems, feedback?

uh, so when i go to play i plug in the cord and turn on the amp and all i hear is feedback ive tried all the knobs none of it works. so me being myself, i unscrewed the part when you plug in the cord, and needless to say the black cord on the inside is disconnected and the white isn't. my guess is that those are pick ups or something, but the black one is broken so, what do i do? btw i have a fender squier strat. i cant play :S andi wanted to try out my new sheet music;-;