Hotpoint rla36 larder fridge not getting cold

[leighgee]

I have a problem and I hope that someone can help! I have a Hotpoint RLA36 Graphite, it's a few years old but in excellent condition except for the problem.
I dont know anything about fridges so please bare with me over my lack of technical knowledge and component names! The light is on and there is a humming sound but it no longer gets cold and adjusting the thermostat switch does not make any difference and doesn't click on or off when moved? I had thought it was the thermostat that needed changing, so I bought a brand new one and changed it (if I have done that correctly) but it has made no difference. The bits on the back (the domed thing and little black box) are hot.
I just wondered if it sounds like something that can be easily fixed or whether it has had it and i need to buy a new fridge? Its just so frustrating, when its not very old. Hope someone can offer me advice. Thanks in advance

[The MG Pony]

Sounds like it has lost the gas charge, but first off are the coils clean?, do you hear a fan running on the inside frezer compartment?

[leighgee]

Hi, there is no inside freezer compartment, just a fridge. The "coils" on the outside back are clean. I think it's beyond fixing, repaid will probably cost more than it would to buy a new one. Thanks anyway