You can troubleshoot electrical problems in your house by using a multimeter to test outlets and by checking for obvious problems. A multimeter is a device that tests voltage, resistance and current along a circuit, enabling you to pinpoint problem spots. If you don't feel comfortable, call an electrician.
Troubleshooting starts with the simplest solutions. First, if you know an appliance works and it stops, move it to a different nearby outlet for testing. This determines if a single outlet is bad or the whole circuit. Then, locate your house circuit breaker panel, usually in the laundry room or cellar. If one of the switches is showing a red section, it means the circuit has been overloaded and caused the breaker to trip. Unplug one or more appliances from the circuit, then flip the switch off and back on. If it quickly turns off again, it means a short likely exists somewhere along the circuit and it requires professional attention.
Next, work with the multimeter. With the circuit on, plug the two leads into their appropriate slots: the red lead goes into the VAC port, and the black goes into COM. Adjust the measurement setting to AC voltage. Place the red lead into the shorter rectangular plug on the outlet and the black lead into the longer one. If there is a reading of zero, it means there is no voltage from the hot wire.