My bonnet always gave me the ****s but usually when it wouldnt open i could just get someone to push down on the mechanism while i pulled the bonnet release lever and it would open.
Now that doesnt even work anymore.
Its really inconvenient as i need to be fiddling with my car now.
I called the NRMA and he got it open somehow.
But I can't do that everytime i need to pop the bonnet.
just fixed the same problem with my brothers car..
to open it i pulled on the cable inside the car with a pair of pliers... needed someone to push still.
i then unscrewed the bonnet catch half a turn or so.. greased it up a bit.. and adjusted the cable so it was tighter. to do that take off the piece of plastic between the radiator and front of car, loosen the 8mm (or was it 10?) bolt, and pull the whole cable till its tight - watch the spring though to make sure it still catches.
tighten it and have someone else pull the release normally, the spring should open all the way.
hope that helps... just be careful when pulling on the bonnet cable with pliers.. my brothers had rubbed somewhere and started breaking.. and i snapped it completely so had to get another :P