I would consider you to doing the following.
- Hold camera upside down in right hand and strike the top sharply on my left hand so there is a cushioned but solid impact. Repeat a number of times. This has the effect of driving the batteries into the body and MAY clear an obstruction.
- Insert a thin stiff metal object at H along the line of the purple arrow. A nail file or piece of still thing spring steel (such as is used on some large wooden boxes as strapping when shipping). The object is to workl bewteen door and hook at H and try to free up the lock sliding action.
- Try levering with a thin metal object between body and door (on outside on body side of A) to try to get the door to move in unlock direction. Tapping the camera kindly but firmly while trying this may help.
- With a dril of about 6 mm diameter drill (Really!) into the door at the outside next to point D so that you can see and access the tip of lock H WITHOUT DAMAGING IT. Once you are JUST through the outer wall of the door you can use a hand held reamer or larger drill (10mm - up to enlarge the hole without damaging the hook at H. This allows you to see if the hook is jammed. Better, if you can cut the ledge away around hook H without damaging H then IF this is the only latch it may allow the door to be opened or partially opened without sliding.
If above method is not suitable for your device then don't be dissapoint just read the article Hadware Troubleshooting under Nikon D700 Manual.