Beko cool64bfd compressor and fan won't run

I've had my fridge freezer 17months. Recently it would run intermittently regardless of whether it was down to temp or not, now it will not run atall. There is voltage to the compressor relay and up to the motherboard, but does not come back from the motherboard to the klixon, despite the fridge stat calling for it to run. I replaced the board, which did not. Stripped the freezer down and checked all wiring, which made the unit run for a while. I replaced the thermal insurance lead(that's what it's called on beko site) but this still hasn't worked. I've linked out the motherboard to enable refrigeration, but obviously this isn't a permenant fix. Anyone have any ideas/experience with domestics. I'm used to big fridges

Turn off at the wall wait 30 secs turn back on and hold the quick cool button for 3 secs that takes you into service mode, every time u press the button it tests another part of appliance each for between 3-5 secs if that fails then board fault

Quick Cool button? Where's that to? All I have on the fridge is a thermostat in the ceiling of the fridge. Am I being blind? I have no tech documents with the fridge. It was a wedding present from the In laws and they "installed it" for me but didn't leave me with any paperwork. Thanks for the quick response.

has it got pcb on the back near top?

Hi there sorry I've not been on here lately. Yes it does have a pub board at the back at the top of the unit. There is power onto the board, but doesn't send voltage back down to the compressor. I replaced the board but it made no difference