I have a roof lining that is sagging in the front by the windshield. Does anyone know how I can stick that back up? Should I just put a screw into it to hold it up?

 

Sounds like the fiber board is warped. You might be able to remove it and steam it back to shape or buy a good used one.
Be careful with a screw. You don't want it sticking on the outside of the roof!

 

yeah, that would look kinda funny with 4 screws sticking through the roof. I have a few short black ones that I measured out to make sure they don't go through the roof. Is there any type of super strong adhesive that would work??

 

3M makes a 2 sided tape-like material for sticking things like the door guards on that will do the trick. Very sticky and permanent.