Engine doesn't start, only clicks...

[bunskippy]

Update: Took the battery to Kragen, they tested it and recharged it. Came back, scrubbed off the white fuzzy stuff with some baking powder and water. as I was trying to screw the bolt back to clamp the pos terminal, the bolt just came apart in the middle. I guess the combination of battery acid and rust was too much. I'm traveling for a week, so won't get to pick up a bolt and try again until then.
I tried it with the clamp just sitting around the terminal (looks like it was making contact, but not as snug as if it were screwed in). Starting just clicked as beforel. I'm hoping that screwing the clamp in will make the difference. Otherwise I'll need to look at the starter...
thx