Will not start, lights flashing

The vehicle was given to use and we were told we had to get in a lock the vehicle with the key fob while inside to crank it. And they were right. Now the key fob is not working and we can't crank our car. The lights just flash. We tried replacing the battery, no luck. I have been told this is a security system malfunction. But how do I fix it? Is there a way to reset it?