What type of computer are you using?
If what Tiffany said doesn't work, I would STRONGLY recommend removing all your mods/markings packs/item packs etc.. This will hopefully solve your problem, but if it does not change your rendering system. For me, when I open FH I have the option to change my rendering system (maybe you don't) and I can switch back a forth. If it does not pop up for you, sadly, I don't remember where you can find it, but believe it sin the options section of the actual game. -(press "esc", "options" then look for it, or when you first open FH before you log in there are the same options.) Hope you get on soon.
If this continues to happen and you have found no solutions, ou could always PM a Staff member who may have more experience with these types of issues and be able to point you to a help thread.
- Shay