I've had this problem a couple of times on Fiesta's it's caused by the latch not being lubricated often enough.Have someone hold the release lever in the open position while you grab the front of the bonnet and push down then pull it up then push it down then pull it up then push (you can see where this is going)Keep doing it VIGOUROSLY and hopefully it will jar the lever free(the spring is having a hard time pulling the cam back because it's dry and rusty).if it opens drench the whole lot in WD and move all the parts till they are free.Good luck.
