I activate the alarm with the key device of my stratus 2000, the horn sounds and the led in the dashboard starts blinking, but if I open any door the alarm wont start. A assume is not the remote since the horn sounds confirming activation. It might be a fuse? or a lose wire?

 

Are you sure it's ever worked in the past? My '00 does the exact same thing, and I came to find out that you basically immobilized the system, but does nothing to "alert" others about a "break in" situation, such as by flashing the lights or sounding the horn. The initial honk is to confirm that you've locked the doors. I have not confirmed it since my doors keyhole is busted, but some have a sensor that if it detects the proper key (grey headed key), it will deactivate the alarm or immobilizer when the key is used to open the door.

Best way to test, is to roll the window down, and pull up the lock and open the door.

If it HAS worked in the past (and congrats for having a factory alarm), make sure that your interior lights are coming on when you open the door. The door plungers are what trip the alarm.

If your alarm is aftermarket, than you should really ask a forum dedicated to the type of alarm system that was installed.