Sounds like you shorted out the audio codec, which means you'll need to either replace the motherboard or buy a sound card. To be on the safe side you should replace the motherboard since you don't know what other damage you caused. The cable you're talking about is for the FRONT audio connections, not ones attached to the motherboard, so if the rear connectors (motherboard ones) aren't working it's not possible to fix without replacement.
You should take it as a lesson on what never to do:
1) NEVER have open liquid containers near a computer
2) NEVER leave the case open except for diagnostics
If you worry about overheating, consider getting a better case and axial blower style GPUs.