I went into Settings->Privacy->Factory reset and checked "Format USB Storage". Then I pressed the button to continue and it prompted for my PIN (just numbers) as usual. Then it said it was formatting the USB storage as I told it to. And then it just shut off. So I started it back up and it prompted for a password (full keyboard; any characters you want).
I don't know what I had set that password to (I haven't used that kind of a password in a while) so now I'm stuck. Going into recovery mode does the same thing. Download mode works just fine.
So now what do I do? Is there some way I can format
/data manually from my computer?
Here's some more info about my device:
Samsung Galaxy Player 4.0
Samsung Galaxy S build.prop
Stock Gingerbread ROM, stock kernel, stock recovery