hang-the-9 :
Only thing that can be is that you did not actually solder things in the same way they were, or the jack you replaced it with was not the same one.
Well I bought a new one, a stereo 3.5mm Jack, and I soldered the Left and Right wires at their places, but there were another 2 wires, not only one, that were copper-colored, so i soldered them together to the "ground" part of the Jack.
Is it maybe that the 2 copper wires had do be soldered somehow else?