Car Alarms: Nissan sentra dead & alarm not working, nissan sentra, hazard lights

Question
Hi,

I'm looking after a friends car, it's a pretty old Nissan Sentra (about 15-18 years old I think).  The other day when I parked it it doubled beeped as I was getting out of the car.  Then when I tried to use the alarm to lock it it didn't respond so I locked it manually.  I assumed the battery in the remote was dying (it had been a bit temperamental over the last few days) so I replaced it.  When I went back to the car to try and set the alarm it still didn't work.  I then tried to start the car but nothing.  There is enough petrol in the car and the battery can't be flat as the interior light and hazard lights still work.  Any ideas what the problem could be?

Answer
If the alarm remotes lost programming, then it may be time
to simply replace the system after 15 years.
Trying to replace those remotes could be
most difficult.

For override, see my past answers for that.
For remove and repair/restore application
go to REMOVEALARM.com and get the notes for
it so you can take it out.

ALARMTEK