My newly converted LPG car just died, what do think is the problem?

One week ago I've converted my 1997 Commodore to LPG, today while i was driving i heard a loud 'bang' underneath the car, i kept driving and then i heard another 'bang', this time the car stopped,there is a hissing noise coming from the bottom of the car, i try to start it on petrol but it didn't work. After trying to start in 2 mins, it finally started in LPG, but the gear seem to be very abrupt, the car trembles. these NEVER happened before the LPG conversion, What do you think is the problem?