what's wrong with my ballast?

[Black Phantom]

The HPS refers to high pressure sodium which a lot of companies use because they're cheaper than some of the other MH types. They do run your MH bulbs unfortunately they only run a certain type of bulb, which limits your selection. It is probably the old "tar" style ballast which are a coil and core and draw a lot of power.
I've found that when they stop working that there's not much to do but buy a new one.
If your not an electrician then you can't buy a ballast over the counter (at least they're not supposed to sell you one) so you have two choices.

1. Get an electrician to redo your ballast (high cost) or
2. Order a new electronic one online and redo it yourself (very easy)

J&L Aquatics is probably the cheapest I've found ($140)and you can usually do the swap in about 20 minutes if your a bit handy. Someone else might know where you can pick one up locally for a good price, but definately go electronic as they will run most bulbs out there.

Hope this helps