Aftermarket security system problems

[CTBMW]

I just had battery replaced, P.O. had a security system installed. He had it disconnected.
I have a key fob that has a button to lock/unlock doors.
Since replacing battery I will get hazards blinking , and car won't start until I turn key and then press button under dash.
Hopefully this makes sense. Any ideas on how to reset?
-Mel