[Fortuna Wolf]

ballasts can be replaced. They tend to be pretty pricey though.

Chances are a capacitor in them blew out. If you can open them up and see a blown capacitor the repair is easy and cheap if you know how to solder.

 

[Fortuna Wolf]

Depending on the type of ballast...
Last time I opened up a fluorescent e-ballast (T8F15, 120VAC in) it had a single coil, assorted capacitors (polymer, ceramic, and electrolytic), 1 power transistor for each light, and assorted resistors and diodes. I'd venture that 80% of the time its the electrolytic cap, and then 10% of the time its the transistor. A busted cap should be obvious.

 

[Fortuna Wolf]

You can unplug it and then short the output the bulb, but really, if the caps are blown it can't store anything and fluorescents don't tend to have particularly dangerous caps.