I won't add similar suggestions as already posted. If these fail, arm yourself with a long screw driver. Look under the hood and you will see the latch and next to it the "striker pin". Have someone pull on the hood release handle inside you vehicle, while you (or better still a third party) gently push the hood up and down. while all this is going on, insert the screw driver under the hood and push against the striker pin form either side until it releases. Once you have the hood open, inspect the plate that the striker pin goes through, and initially spread some grease around it, or you might just undo the bolts holding the plate and slightly re-align it. As a tip in the event of future hood opening problems (when you don't have the extra hands available), such as solo off-roading, tie a thin piece of wire around the hood release catch.
Hope this helps.