Its not freezing!! keeping things cool, but not freezing

my electrolux upright freezer EUU6174 is not freezing. There is power, it is managing to stay 'cool' but not freezing food stuffs. There is a red warning light on the front panel, which I believe is just to inform you that the temperature is not cold enough to store food. I have 'trouble-shot' as in cleaned the air intake, defrosted it, bu the problem remains unsolved. Is there a possible thermostat problem/ fan problem or will I need a new one?? Pete