it is possible that something broke or bent.
if you really want to know if it is the connector on the front of the case, you should get some 3.5mm connector with some cord attached to it (you can buy these or cut something old)
sometimes you will find only mono wires, so if you want to check both left and right .. you'll need a stereo wire with a stereo connector.
you plug in the cord and put one probe on the wire coming from the 3.5mm cord.
then you can put the other probe on the connector in the backside of the case.
or
you could connect your audio connectors and put the probe onto the metal of the other end of that cord that usually plugs into the soundcard or motherboard somewhere.
i dont know if the cable that goes from the front audio panel to the motherboard is sealed with molded plastic or if there are header pins with a removeable connector.
either way.. you will put one probe on each end with the multimeter dial set on the ohms setting.
if you dont have a multimeter, you can get a cheap analog one from a local store.
usually these wont tell you what ohm it is, but if there is a connection .. the needle will jump all the way to the other side to give a clear notification that it is working.
if the front panel comes back as working.. then you might want to look inside the connector to see if any of the pins/connectors are bent/loose.
you should have your problem narrowed down to the culprit real soon this way.
those analog multimeters are only like $10 - $12 (maybe $14)
but
they come in handy for other things too.
bad connections are only one thing.. a battery tester helps, and so does reading voltage.
to help you not feel so bad, maybe the cord that goes from the motherboard to the front audio panel is degrading some of the audio quality?
and maybe it is better that you use the rear of the soundcard since it is closer to the actual outputs.