Either way if you had the doors opened a lot, it should like you probably have frost build up preventing proper air flow. You'd need to pull everything out of the freezer and remove the lower back panel inside the freezer. If there is frost build up, you'll need to use a hair dryer to thaw all the frost out. The unit will continue to beep until the set temperature (0 and 38) are reached so that could take a while even after thawing out all the frost build up.
If removing panels sounds like more than you can handle, you can always unplug the unit for 24 hours and leave the doors open to allow the unit to defrost on it's own.
A Freezer usually has a condensor drain coming out of the compressor, that empties into a condensation dish underneeth, where condensation water is picked up and Re-evaporated.
It is most likely that your Drain is clogged.
Happened to me.
Have someone check your Drain, and if needed unclog it with a small prying tool into the tube.
