My refrigerator freezer is running, but it is not cooling

It probably has a leak in the coolant system or has run out of coolant, I would have it serviced.

The problem is very common with some freezers.
It has run out of GAS.
It must have a bit of a leak in the gas system.
Get a professional to re-gas it.
Saves you from a big investment in getting a new freezer.