Listen for sound from the freezer -- power is reaching the appliance if you hear the motor running. Most freezers run a defrost cycle several times a day to reduce frost and ice on the walls and shelves. During this time, the freezer may make a hissing sound -- this is normal. Listen again for the motor in 30 minutes in case the freezer is defrosting.
Go behind the freezer and check that the power cable is still in the outlet. It's easy to knock the power cable loose in the outlet while you are cleaning behind the freezer. Without power, the freezer will start to defrost and spoil your food. Power supply issues are one of the main causes of food spoilage.
Turn up the thermostat for more cooling power. The freezer could be set too cold for food to be properly frozen and preserved. Your freezer compartment should be at 0 degrees Fahrenheit (minus 17 degrees Celsius). Use a freezer thermometer to help you achieve this temperature if your appliance uses a numbered or alphabetical thermostat dial.
Check that the power outlet is still working. You may have switched off the power or blown a fuse in the circuit. Go to your fuse box and change any blown fuses with suitable replacements. Plug the freezer directly into an outlet, removing all power bars and extension cables. Contact an electrician if you are unsure about changing a fuse.
Take a look at the rubber gaskets attached to the lid. Ensure the gaskets make contact with the freezer at all points around the door frame. Keep an eye out for signs of damage or corrosion on the seals. The freezer will warm up and defrost when air is allowed to enter from outside the appliance.
Ensure that all food and storage containers are below the freezer's rim. Items above the rim will hold the door open and allow warm air to enter the freezer. Re-arrange your food so the door closes tightly. You may notice the appliance freezes up if room temperature air is entering the freezer.
Contact the manufacturer if you continue to experience problems with your chest freezer. There may be a technical failure within the freezer causing it to malfunction. Ask about your warranty options when you reach the manufacturer.