can't get default controller to work

[eluser]Unknown[/eluser]
I'm getting started with CI. I just installed, but I can't get the default controller to work. I tried with no file modifications at all, and after setting the base_url config.

The default /welcome works, but going to the base url generates "No input file specified."

Double checked the routes setting and it's set to the default "welcome". I also tried with a different controller, but the same thing happens.

Anyone have an idea what's going on? Thanks.

edit: I'm using Dreamhost