ENGINE ONLY TURNS OVER EVERY FEW TRYS?

I HAVE A W REG SPRINTER 208 CDI SWB, WHICH WHILE SAT AT LIGHTS SUDDENLY FILLED WITH BURNING PLASTIC SMELLING SMOKE. AFTER GETTING THE VAN HOME IT TURNED OUT THAT THE STARTER MOTOR HAD BURNT OUT(ALTHOUGH IT WASN'T BEING USED AT THE TIME) AFTER REPLACING THE STARTER, I FOUND THAT THE VAN WILL ONLY START EVERY FEW TURNS OF THE KEY, SOMETIMES TURNING OVER FINE, AND SOMETIMES NOT EVEN A CLICK. WHEN IT DOESN'T TURN OVER ALL DASH LIGHTS GO OUT AND WON'T COME BACK ON UNTIL THE KEY IS REMOVED AND INSERTED AGAIN, IT STARTS ABOUT 1 IN 3 TRIES BUT I'M AFRAID OF DRIVING IT IN CASE THE INTERMITTENT PROBLEM IS WHAT CAUSED THE STARTER TO BURN OUT IN THE FIRST PLACE AND IT HAPPENS AGAIN! ANY ADVISE OR IDEAS WOULD BE GREATLY APPRECIATED!