I have this every since installing my honeycomb grill, dont know why, there is no obstruction.
I Press the lever really hard, it will almost feel like its going to break, but dont go that far.
Go to your bonnett and you should feel it open a little, pull it up, then go back into the car and pull the lever hard again, this should release it.
When you get it open check the spring and and metal clamp that is around the bonnett release clamp to ensure it has not snapped or has a crack.
Trace the cord as well, maybe you have a kink or break, but this is doubtful as you would not be able to get it open if the release wire has broken completely
What year is your car, the cords degrade over time and can stretch a little, this could hinder the release.