Edits don’t save

I just installed WordPress. Changes to the configuration don’t save. Edits to the first post don’t save either.

What puzzles me: when trying to edit the standard first post, I get an empty post to edit. If I enter text there, it still doesn’t save in any way.

When I try to save one of the configuration options, I get a long page listing all options. But the changed option does not stick.

Edits directly to the database through my phpMyAdmin work as expected. Could this have something to do with how the webhost has configured PHP?