Headlight on drivers side won't work but high beam works.. Why? Toyota celica gt 1992

Check for loose wires or a break in the wires somewhere , End corroded terminals on the plug, If that doesn,t work , Get a diffferent relay.

ck connector for bad contact and power, if no power headlight switch may be fault would have to trace system for voltage .

I would check for voltage at the dimmer switch first.

It sounds like a bad bulb

Have you checked the light globes ? The globes have a filament for each of Low and High Beams and the Low Beam ones fail much sooner than the high. A bump as you describe may have been enough for the Low beam filaments to fail as the filaments get brittle through age.

The globes filament for low beam are most likely both blown . Check if the plug is getting voltage when the low beam is on or buy a replacement globe and check if this is the case.
How do you know both low beams stopped at the same time ?
They most likely blown at different times but you notice it when both go out and you have zero light. Had this happen to me on a ford falcon EA . Was the globes.
Try not to handle the glass on the replacement globes if Halcyon globes .

The adjustment screws/nuts should be located either on the top of the headlamp assembly, behind the headlamp assembly, or near the frame rail by the radiator support.

You will have vertical adjustment screws for each independent beam (separate highs and separate lows, but will be same screw if highs and lows are the same bulb). You may also have additional horizontal adjustment screws as well

Park your car on a level ground 30 feet from a wall and measure the height from the ground to the bulb and mark on a wall (do this for highs beams and low beams if the bulbs are separate, if highs and lows are the same bulb, only do it for the lows)

For Low Beams: If the headlights read VOR, then aim the brightest part or cutoff part just below the mark on the wall. If it says VOL or nothing, aim them 2 inches below the mark on the wall.

For High Beams (if separate from low beams): Aim the headlight directly at the line you marked on the wall.

The adjustment screws/nuts should be located either on the top of the headlamp assembly, behind the headlamp assembly, or near the frame rail by the radiator support.

You will have vertical adjustment screws for each independent beam (separate highs and separate lows, but will be same screw if highs and lows are the same bulb). You may also have additional horizontal adjustment screws as well

Park your car on a level ground 30 feet from a wall and measure the height from the ground to the bulb and mark on a wall (do this for highs beams and low beams if the bulbs are separate, if highs and lows are the same bulb, only do it for the lows)

For Low Beams: If the headlights read VOR, then aim the brightest part or cutoff part just below the mark on the wall. If it says VOL or nothing, aim them 2 inches below the mark on the wall.

For High Beams (if separate from low beams): Aim the headlight directly at the line you marked on the wall.

Replace the headlamp switch assembly

Have you checked the fuses?  1 fuse panel in the driver side area of the car, and there may be 1 under the hood as well (usually near the battery).