Some basic stuff: Nothing stolen from under the hood? Is the battery charged? (turn on the headlights to check, they don't depend on much under the dash.) Ignition switch in place and working?

Then like the others said you'll probably need to carefully de-install what is left of the alarm and restore the wiring to stock. Disconnect the battery before working on wiring.

 

I wonder if it was a command start, and now, the starter wire isn't connected. Just a thought.