Set prime rib out 30 min before cooking. Preheat oven to 500. mix together about 1/2 cup each salt and pepper. Add garlic powder to taste. Rub all over roast so it will form a crust. Put in roasting pan and cook at 500 for 15 min. Turn oven down to 375 for 45 min. Turn oven off and do not open. Leave in for 3 hrs. Turn oven on to 375 about 30 min before serving. Remove from oven and let it rest before slicing.