Pc world faulty laptop help!!totallly unrepairable?

need advice to sort out pc world.. got an advent laptop jan06 needed to be repaired by march, since been in 2 more times with different problems and twice for the same problem which they did not fix, it is now 17 mnths old and i have an independant report to say it cannot be repaired, also still paying for laptop through pcw arranged finance(nearly3yrs left). it adds upto around 8-900 pounds .what can i do?it is obviously not fit for use.