Both headlights on your car are out and won't come on -- it's time to troubleshoot! If both headlights are out at the same time, the problem is likely to be electrical. To troubleshoot, start with the easiest thing to fix and work from there. Even if you manage to get the lights working again, check other potential problems to prevent a recurrence.
Inspect the headlights to make sure the filaments are not broken. Remove each headlight from its housing and check to see if the filaments are intact. If not, replace the damaged bulb. Don't touch any part of a Halogen replacement with your fingers except the base. Oil from your fingers on the glass bulb can cause the headlight to fail prematurely. If both lights are out, replace them both. Check to see if the new headlines are working.
Check the headlight fuses in the car's fuse box. Open the fuse box and check the headlight fuse. If the fuse shows as burnt out, replace it and test the headlights again.
Check the connectors, wiring harness and socket into which the headlight bulbs are plugged. Look for rust or corrosion around the connectors and wire harnesses. Also, look for wires that have pulled loose. Replace the connector harnesses, wiring or sockets if there is any sign of damage, wear, looseness or corrosion. Make sure the ground wire from the light socket housing to the car frame is making a good connection.
Pull out the headlight relay if the headlights still do not work. Shake it. If the relay rattles, it needs to be replaced. If the system uses a control module instead of a headlight relay, you'll need to consult your vehicle repair manual to identify the module. Check to make sure power is reaching the module. If it is and the headlights still don't work, replace the control module. The lights should come on.
Replace the headlight switch if there is no power reaching the headlight relay or control module. The headlight switch is probably broken and needs to be replaced. Get help with this one from your dealer, especially if the switch is in the steering column. You could set off the airbag and injure yourself or damage the vehicle.
Disconnect the power from the battery when not testing the circuits, especially if you are working around the headlight on/off switch. You could trigger the airbag and injure yourself or damage the vehicle.