RENAULT LAGUNA PROBLEM?

I HAVE JUST BOUGHT A 1.9 DCI LAGUNA ESTATE 53 PLATE BUT IM HAVING A PROBLEM WITH IT IT STARTS OK BUT I THINK ITS LACKING POWER WHICH I CAN LIVE WITH BUT THE PROBLEMS IS AFTER ABOUT 5 MINS OF DRIVING THE HEATER PLUG LIGHT COMES ON AND CAR HAS NO POWER DOES ANYONE KNOW WHAT THE PROBLEM COULD BE , THE TURBO WAS REPLACED IN 2006