Battery issue

I have a '96 Jetta GL. I disconnected the battery to do some work inside the door panel. When I re-connected the battery, the car would not start. When I turned the key in the ignition, the anti-theft mechanism went off (all lights blinking). I shut off the alarm by locking/unlocking the doors, but when I tried again to restart the car, again the anti-theft mechanism went off.

I shut off the car, let it sit and when I came back to it, when I unlocked the door, the interior light blinked on and off at first before coming on solid. When I tried to start the car this time, the ignition clicked but would not turn over.

Any idea what the problem is? Does the battery have enough juice?