if its been a really hot day and you been driving a bit try putting it somewhere cold (shadE) and may be cool the bonnet with water and in theory should help tighten the cable a tad allowing u to pop it up and then readjust the cable
:)
August 2011
I had the same problem I have to pull the bonnet release until the spring clips under the bonnet then pull the bonnet up and down until it opens. Make sure the bonnet release cable is in it's holder sometimes it can slip out.