There are several reasons for “Trouble” or “System” to be on. Please consult your user manual as to how to display Trouble or System. Some “troubles” report codes and some do not. You can arm the system even though the trouble light (or system light) is on.
“System” light is an indicator of up to three items, - Trouble status, Alarm in Memory or Bypass. Again, you will have to consult your manual to find out how to evaluate the problem. Check your user manual.