You probably solved it by now. But just in general: soldering needs to be done neatly. And any electrician connection needs to make good contact. To fix the problem you need a multimeter to measure if you get 12 volts at the connecting wire. If not maybe the fuse is gone. If you do get 12v, then measure at the top of the board. If not, the soldering might be bad. If you do get 12V, then any component on the led strip might have become unsoldered or the strip might be broken. If so, put in a new piece of strip.