What do i need to replace?

I have a Schriber integrated freezer (app 6403) the warning buzzer started going to warn me that the freezer was not holding its temperture I turned it off and transfered the contence to my other freezer.
The next day I turned it back on it ran ok the motor was switching on and off I placed some water in it which did freeze, then after about 27 hours the same thing happened again.
Whats the problem ?