My strings on my strat body guitar seems loose on the fretboard like it lose tension?

i was bored one day and i decide to unscrew the back of my guitar plate off, not knowing that it was holding the neck up and the neck and the neck was just supended in air, the only thing holding it was the strings witch went way outa tune so i tighted it back and tuned it up and i notice the strings on my guitar lose tension and seemed loose and not tight. what happened? how do i get my strings to get that tension back, what do i need 2 screw tighter. this guitar has a fender strat body