Stuck in an install loop

When installing a fresh phpBB on my server (the server as never been used before), i encounter some weird bug : i log into myIp/install on my firefox browser, click install. It goes through the requirments, like it's supposed to, then I have to fill out the first form. It works perfectly, but when comes the second form, no matter what i fill in, the submit button brings me back to the first form, without an error message.