1In ungreased 3-quart microwavable bowl, mix frozen potatoes and water; spread evenly in bowl. Cover tightly with microwavable plastic wrap. Microwave on High 15 to 20 minutes or until potatoes are hot and tender, stirring once halfway through cooking.
2Add vinegar, mustard, salt and pepper to hot potatoes; mix well. Spread evenly in bowl. Cover, refrigerate at least 5 hours or until completely cold.
3Meanwhile, in 2-quart saucepan, place eggs in single layer. Add enough water to cover eggs by 1 inch. Heat to boiling. Immediately remove from heat; cover and let stand 15 minutes. Drain; rinse with cold water. Place eggs in bowl of ice water; let stand 10 minutes. Drain. Peel eggs. Reserve 1 egg for garnish; chop remaining 4 eggs.
4Stir mayonnaise into cold potato mixture. Add celery, onion and chopped eggs; toss gently to mix. Spoon mixture into large serving bowl. Slice reserved hard-cooked egg; arrange on top of salad. Sprinkle with paprika. Serve immediately, or cover and refrigerate until serving time.