When you say "does only floor vents", do it mean it will blow out the floor vents all the time, regardless of the vent control setting, or only out the floor vents when set to floor and no other vents when you change the setting? Are you sure you're not getting air out the defrost?
You HVAC vents operate on vacuum. There are vacuum actuators under the dash, behind the glovebox that open and close the doors and direct air out the selected vent.
If you have a vacuum leak upstream from the vent control, you loose all vacuum causing the doors to default to defrost.
In your case, sounds like you either have a leak downstream from the control, or perhaps some obstruction blocking the actuators. Perhaps the actuator rod broke or simply slipped off.
When you pull the control panel out, you'll see the vacuum connector. Make sure it's secure, and all the lines are intact.