The "round, gold colored" piece is the thermostat wafer. There should be a micro switch attached to it, as well. It is the heart of the unit and if it's not complete and working correctly, you have only a bad beer cooler.
DO read the instructions. Follow them if you like, or if you really want to do this right, do the following:
If it still has the red-liquid filled bulb thermometer - throw it out.
Get a digital, remote probe thermometer, a water-filled tube squeezy toy and a simple hygrometer. Then check back with us before you do anything, so we can tell you what to do with this stuff...