My name is Peter. I am a retired field service refrigeration technician.
You did not provide a model number. The model number is on a label, on the liner inside wall of your fresh food section near the top.
I picked a Superba 48 model number at random to see what you have. The model I picked - the control boards are not available. But these are not your problem.
Every 8-10 hours your unit completely shuts down except for the lights, and goes into a defrost mode. This is where your defrost heater turns on for 20-30 minutes, defrost your cooling (Evaporator) coil, and then turns your unit back on. You may have a bad defrost timer.
1.) Defrost Timer - Behind your unit is a defrost timer.
The timer is mounted on the back a steel bracket with a hole through it. Take a flat head screw driver, turn the round shaft one click at a time clockwise until the unit turns on and is running.
If the unit turns on, then you have a bad defrost timer.
Note: When replacing note what contact number the black wire is connect.
2.) Power On/Off Switch - In the lower back, you also have a Power On/Off switch. Unplug the unit disconnect the 2 wire leads on the switch. Using a multi-meter, set ant the lowest Ohms (Omega Symbol), Ohm out the switch. If you get a reading other that '0', then the switch is bad.