Sorry to bump an ancient post, but I had this happen last night during some unrelated maintenance.
Had the hood up, closed it to move the car, went to open it back up and there was no tension whatsoever on the hood release lever inside the cab.
Tried yanking the lever, mashing on the hood, getting at the latch from underneath the vehicle, etc. The cable had slipped off the latch mechanism under the hood, so no amount of yanking on the cab lever or smashing the hood down would've worked.
Ended up removing the three lower screws on the front grille and prying it forward as much as possible, trying not to break the upper tabs. Was able to create an opening between the bumper and grille juuuuust wide enough to get a socket in there and remove the three latch mechanism bolts. I was fully expecting to break the grille, but surprisingly it held up fine.
If you've got no tension on the release lever, removing those bolts is your only option. Cross your fingers, have a drink, expect to break some grille tabs, but with a little patience you might get lucky and not snap anything.