No crancking or starting

Hi

I have an Audi Q7 4.2 TDI, BTR engine. At some stages when starting the vehicle there was a "clack clack" sound on the hydraulic lifters. I added an additive and after about 50km's the sound would disappear. One day I was driving from my home to the local mall and the car suddenly lost power and since then I could not get the motor to crank over, let alone start. There was no sound, warnings or lock up of wheels when this happened.

I have replaced the battery, all relays and fuses have been tested, diagnostics does not give any real indication of what the problem could be and I have tried turning the crank by hand with a socket, but it does not move.

I'm guessing it could either be the hydraulic lifters or maybe the timing chain, but I'm no expert in this field.

Would highly appreciate any assistance or advice you might be able to share with me.

Kind regards