Sounds like the plastic clip joining the lock to the bonet catch has come apart. The only way you can open.the bonnet is.to either use the key and push it.in harder and wiggle hoping.it will grip and unlock or try and get up behind the catch and undo.the two 10mm bolts that hold it in place. It can be done that way but is a little hard.

Why did you take the grill out to remove.the headlights?