Check the battery and cable connections. How bright is the dome light or head lights? Do they start out bright but go out when you try to crank the engine? If so, measure the battery voltage with an inexpensive digital voltmeter. It should be 12.6 volts. If it's closer to 12.2 volts, it's good but discharged. If it's around 11 volts it has a shorted cell and must be replaced. If the voltage is okay, measure it right at the starter. Also check the smaller negative battery wire where it bolts to the body. Be sure that connection is clean and tight.