help

Hi I am in need of help went along drive yesterday helping family members out but I have gone to use the car today and it started fine but I have no acceleration max 1200 rpm and loads of black smoke and eventually knocking getting louder.she is a mk2 Laguna,2.2 diesel, automatic, 120000 miles,any help much appreciated,I'm aware that the car is not worth a lot hence wanting to take into a garage and rack up a massive bill,just strange how ran perfect yesterday ,thanks again.