What's wrong with your upright freezer?
We'll go over some common issues and mention the parts that might be causing the problem. You could potentially diagnose some of these issues yourself. However, without a multimeter on-hand your flexibility will be limited.
First off, is your freezer not turning on at all? If so, this problem is likely due to something from the power supply or source. Check to make sure the power plug didn't fall out of the outlet. Make sure the fuse didn't blow or the breaker didn't trip. Lastly, ensure the correct amount of voltage is coming through the outlet - contact an electrician if you get an incorrect reading.
Does your freezer power up but not operate at all? Try vacuuming the coils to see if it's due to a simply obstruction. If that doesn't help, next it's time to see if there is a lack of continuity in any of the key parts that make the freezer run. Test the evaporator fan, defrost timer, compressor motor, temperature control, etc.
Is the light not turning on but everything else seems fine? If so, either the bulb is burnt out and needs to be replaced or the switch is defective and needs replaced. This kind of freezer problem is very easy to fix and can be considered a DIY job for most appliance owners.
Is the freezer simply not reaching a cold enough temperature or not holding a freezing temp? In that case, the issue could be anything from a weak or broken door seal to a defective temperature control, obstructed drain tube and much more. This kind of problem in an upright freezer is almost always best left in the hands of a freezer repair professional.
Sometimes a freezer will stop freezing its contents. This issue is often the result of a lack of proper maintenance. You can check your condenser coils to see if dirt and debris is covering them. It's possible for the freezer to stop maintaining a freezing level temperature if there's too much dirt on the coils. As you would guess, simply cleaning them will fix this problem. If cleaning does not remedy the issue, the next two things that you should check for include a defective start relay and evaporator fan motor.