Maybe the switch is wired wrong and you're shorting-out the power? Maybe the switch wiring or the logic is backwards? Did you try [u]Digital Read Serial?[/u]?
But, how do you know "the sequence" is stopping?
Did you write the whole program without testing anything? You should "develop" and test your code a few lines at a time.
Do you have anything connected to simulate the outputs (horn, hazard, etc.)?
In addition to monitoring the outputs, some [u]Serial.print()[/u] messages to the serial monitor, such as "Door Open", "Door Closed", Sounding Alarm", etc. That way you can "see" what your program is doing. You can also print-out your timer states, etc.
And, for debugging purposes you can shorten your delays.