1998 Hyundai Excel Immobilisor no longer works and I can't

I left my lights on and battery went flat. Road side assist came to jump start my car and when they put the jumper leads on I pressed my immobilisor before I turned the ignition and my immobilisor didn't work.. This hadn't happened before.
The red light on the right dash that usually flashes is dead. Has my alarm cut out?
What are my options in fixing it. Disable the alarm? Replace the immobilisor system?

The Road side assist fella ended up hot wiring my car so I could drive home. I tried the immobilisor button again when I got home but there was still no movement.

Any help appreciated.
Ingrid.