If you faced a similar problem in the cold season is likely to cap gas tank just froze to the body. Especially, the probability that, if you find a problem in the frosty morning, and the day before passed precipitation in the form of rain.
To open the frozen lid of the tank, it is enough to pour hot water and try to reopen it from the salon. If no effect, try gently tap a hand on the lid of the tank and try again.
If the lid is still closed, try to lock the lever opening the lid of the tank in a raised position, placing it on any suitable subject, and repeat the procedure, pouring and tapping. If the lid opens with a button, ask someone to help you press the button, when you will try to open the cover on the outside.
In the case, when it's warm, and there is no reason to consider the cover frozen to the car body, the problem may be the cable is broken, with which she opens. If the lid is opened by pressing the button, check the fuse – maybe he burned out, and this was the cause of failure.
If the fuse is intact, or cover open lever, you can try to open the lid from inside the trunk. It will have to remove part of the skin and, reaching a hand to the rope, pulling it with his hand. The lid should open.