The most common cause of a falling closet is loose screws or nails. Check all of the screws and nails that are holding the closet to the wall, and tighten any that are loose. If any of the screws or nails are stripped or damaged, replace them with new ones.
If the wall is not strong enough to support the weight of the closet, you may need to reinforce it. This can be done by installing a new stud in the wall, or by adding a metal plate to the wall.
If the closet is still not stable, you may need to add additional support. This can be done by installing a new shelf bracket, or by adding a metal rod to the closet.
If the doors of the closet are not hanging properly, you may need to adjust them. This can be done by loosening the screws that are holding the doors in place, and then moving the doors up or down.
If the hardware on the closet is damaged or worn out, you may need to replace it. This includes the hinges, screws, nails, and shelf brackets.
If you are not comfortable repairing the closet yourself, you may want to hire a professional. A professional will be able to quickly and safely fix the closet, and they will also be able to provide you with a warranty on their work.