LPG problems

Well, it was all going to plan until today when I switched over to gas and nothing happened
It was working yesterday and there is gas in the tank so I was wondering if there is something simple I could check.
The pump can be heard clicking in when switching over. I will check tomorrow to see if there is any gas at the manifold but meantime has any one any ideas ?
Ta

hi when you say the pump can be heard switching over ? my freelander has just stoped running on gas just beeps and swith light is blinking been in a garage but couldent find fault ?