The simple answer may be that the low beam side is burnt out. Replace the bulb.
However, if both headlights have stopped working when switching to low beams, there may be a problem with the relay or the switch itself. If the cost of a relay is low for your car, it may be less expensive to simply replace that component than to have it diagnosed in a repair shop. Replacement of the switch requires some disassembly of the steering column or dash in most vehicles. Check a specific service manual.
Bulbs burned out?
These lights have 2 different "lights" in each of them. This occurs frequently. Change out the bulb and everything will be working fine once again.
All of these parts run on electricity, and for all of them to fail would be bad. Bad or burnt wiring could cause them not to work, or a alternator going bad could cause them not to work as well.
burned out bulb, blown fuse, wiring
The light control module could be the cause of hazard lights coming on after the car is turned off. There could be a problem that has caused this module to become wet and it is now not working correctly.
If parking and tailights are working could be headlight switch--rheostat for dimming control could be bad
The dim lights on a 1994 Grand Prix could go out when the headlamp switch is on if there is a short in the wiring for the headlights. There could also be a problem with the bulbs themselves if they were touched during installation. The oils in the fingers can short out new headlights.
Yes, in the fuse panel. Open and read your owner's manual.
If the back lights on a Peugeot 206 are not working, make sure the bulbs are new. If the bulbs are not the problem, there could be an issue with the fuse.
The bulb could be 'blown'. Remove the working bulb from the other light and try it in the socket of the one that isn't working.
If you brake lights are not working on your trailblazer it could be due to a number of reasons. Your fuse could be blown, or your light may no longer work.
If the motors are working, then there has to be a problem between the motors and the lights. If they are only "working" though if you bench test them, and they don't actually do anything when you turn on the lights, then there must be an electrical problem such as a break in a wire or a bad ground to the motors.