1999 Volkswagen Cabrio 4 cyl 85000 miles

My alarm went off, tried to unlock driver door with key. The whole locking cylinder came out. I put it back in. Disconnected battery to temporary stop alarm. I realized that I could unlock trunk to stop alarm. Did so, reconnected battery. Car started but when I try to drive it just cuts off. It will only stay on if your foot is on gas or if it is just sitting still in neutral.