Hood will not shut - 2009 Mercury Mountaineer

If you mean the hood will not lock down in a closed position the following applies.
It can be due to a stuck hood release cable or latch pivot that is out of sequence. With the cable problem, the cable remains pulled back in an OPEN position and the latch pivot will remain in an unlock position under the hood. For the latch pivot, the pivot has a V notch and is suppose to lay in an open position in order for the hood striker to trip it into a locked position. You may not be lined up, basically the pivot is flipped into a closed position and the striker hits its' top instead of its' V slot.

Rust or a broken pivot return spring can be the causes for this defect.

If you mean the hood will not move down from an open position, then that is a different problem. The small lift cylinders on each side of the hood may be jammed. Or the hood hinge could be defective. Be careful, some hoods are made of aluminum and bend easily if forced.