I have an Oasis water cooler and just encountered the same issue. It turned out that the water in the tank had frozen. I searched all over for a manual and the only one I found was useless. I called the dealer and they said, "Unplug the unit, wait for it to thaw, then plug it back in." (Great solution, unless it just happens again and again!) So I asked, "what if it keeps happening?" They told me to turn the thermostat down (clockwise), so I thanked them and went to do that.
Surprise, I couldn't find a thermostat on mine. Yours may have one, though!
I suggest unplugging the unit for a while (giving frozen water time to thaw), then look for an adjustable thermostat. If you can find it, turn it counterclockwise a little bit. Then plug the unit back in and see if that takes care of the problem.
P.S. I realize you may not have waited 2 years for an answer, but, like me, someone may come along with a similar problem later. Hope this helps!