A new receptacle is inexpensive and easy to install, so don't hesitate to replace one that is cracked or caked with paint. If a receptacle fails to deliver power, shut off power to the circuit, pull the receptacle out, and make sure all the wires firmly connect to the terminals.
If you have to replace an outlet, it's a simple matter to replace a three-hole outlet with another three-hole outlet. Replacing a two-hole outlet may be another story, as two-hole outlets are no longer available. If there's a ground wire in the box, you can install a three-hole outlet. If there's no ground, however, it's against code to put in a three-hole outlet. Install a GFCI instead. Although it doesn't protect against a ground fault, its monitoring circuit gives you the same protection you get from a ground wire.
About 30 minutes to remove a receptacle and install a new one
Screwdriver, side cutters, strippers, long-nose pliers
Stripping wire, connecting wire to terminals
Lay a towel or small drop cloth on the surface below the receptacle.
Receptacle, wire for pigtails, electrician's tape
Strip the wire ends and bend them into loops. Connect the black or colored (hot) wire to the brass terminals and the neutral (white) wire to the silver terminals on the new outlet. Connect the ground wire, pigtailing it to any other ground wires in the box and to the box, if it is metal.
If there's no ground wire in the box, replace a two-hole outlet with a GFCI. Attach the black and white wires as you would in a normal GFCI installation. There is no ground wire, so simply tighten the ground screw as far as it goes. The GFCI gives you the protection a ground wire does, but not full GFCI protection. Code requires you to place a sticker on the outlet indicating that the outlet is not GFCI protected.
If a receptacle has more than two wires connected to it, look at the tab that connects the two hot (brass) terminals. If it is broken off, the receptacle is split, meaning either that it is on two circuits or that one half is switched. Break off the tab on the new receptacle and wire it like the old one.