My bonnet would open slightly from pulling the release in the footwell, but the latch wouldn't move so couldnt open the bonnet properly. I prised the latch open with a screwdriver (carefully tho!) from the bonnets slightly open position, and when it was open properly I sprayed the whole mechanism with plenty of WD-40.
Its been fine since then, so if your release handle inside works, try and open/lubricate that latch, could just be dry and stiff mechanism.