how can i fix my car alarm on my 200sx?

when i press the button on key fob to close the car it does not work which means i cannot open it too start the car i have changed the battery in the fob and still no joy. i have had the fob tested it it is working fine, i have also tried some of the ways to reprogram the fob but still nothink is there any way i could get it started any other way