How can I fix my hotpoint FF187E fridge freezer?

The freezer works well but the fridge stopped cooling down. I checked out on the internet and found that sometimes the pipes which force the cool air up into the fridge from the freezer gets blocked with ice so following the instructions I defrosted and hit the back of the fridge and freezer walls and air vents with my hairdryer - hurrah it worked and the fridge started to keep cool again. That was about 3 months ago - to my despair it happened again but that remedy doesn't seem to work this time and it sounds like the motor on the fridge keeps stopping - please help I cant afford to replace or pay for an engineer at the moment.