Electronic Alarms and Home Security Devices - DSC PC2500 Siren

Hi,
We have lived in our 25 year old home now for 5 years and have never used the DSC pc2500 alarm as we were never given the code to arm/disarm from the previous owners. We have always just ignored the many lit-up zone lights on the panel especially since we replaced all the windows last year. Today we came home to both an exterior bell and an interior siren going off. As we are A) so unfamiliar with the system and B) unable to control it at the keypad, we cut the wires to both of these 'noise makers'. I have spent some time this afternoon downloading the manual and installation guides, but we are unable to clear the LED lights for zones 3, 4 & 5. Also, Memory, Shunt and Trouble are lit up as well. I have learned that TROUBLE is related to (1) which is the Battery (probably why the alarms were going off) and that MEMORY is related to (Fire), which I don't understand. If we re-wire the alarms, I imagine that they will just go off again since we are unable to clear our system at the keypad. I have pressed *8 2500 (as you instructed in a previous thread) and was lucky enough to see the ARMED light go on and the PROGRAM light flashing. I entered 19 and then a new 4-digit code. Does this mean I have successfully changed the master code? And if so, how can I clear the pad to READY and potentially use the system I have never once used!

Oddly, we also just discovered that the clock on the microwave and my daughter's digital clock in her room were both flashing, as if we'd had a power failure while we were out. I wonder if that had to do with the siren being set off. Strange.

After 5 years or longer, yes you should replace the battery. As far as your zone lights you either have to repair the wiring/contacts at the windows or jump out (bypass) the zones in the panel with resistors. 1000 ohm If I remember correctly.
Yes you have successfully changed your master code. After you take care of the above, and your system has a ready light. Arm and disarm the system to clear memories.
If the trouble light doesn't clear right away, Arm the system and wait for the green light to shut off, then disarm.

Thanks for the info!
Not sure how to jump out the zones with resistors, but this might make sense to my husband. Our windows were replaced last year so I imagine bypassing will be our cheapest option.
Thanks again!

Take the wires off of the zone terminal and common, put one end of the resistor under each screw and tighten them.