I have a 2005 Prius. My driver side headlight just stopped working. Usually when it's the bulb I get a bit of a warning, but this time it worked one day and not the next. I replaced the bulb and still nothing. I checked the fuses and both are good. Do the ballast's just die like that? Should I be looking at other issues possibly before I replace the ballast?
Current mileage? HID or Halogen? Try swapping a known good/bad bulb around and see what happens... old bad bulb in passenger side, good bulb in drivers. Have you checked for voltage already?
It's HID, about 235k miles. Didn't switch bulbs from passenger side, but I did install a brand new bulb and it didn't work. Not sure on how to check the voltage.
I've had decent luck using generic HID bulbs before, from where and what brand did you purchase? You might try the old working bulb from the passenger side, if it doesn't work on the drivers side then the problem is upstream. It could be the connector socket, wiring, ballast, etc.
I've actually had bad luck with the generics so I have been replacing with the Philips when they go out.