Have you installed any mods recently that mess with dialog/menus etc such as UI replaces or have a warning in them that they may do the problem you have described?
As for a possible fix, you could try using the verifying integrity of game cache local files option in steam in case something is missing from your fallout game files, and it will be auto downloaded if it is. If that doesn't work, and if you have mods installed, try uninstalling them one by one to see if any mods you do have are causing it. If none of these possible solutions work, you may have to re-install it.
I spend my time watching youtube, playing mods for Fallout 3 and NV as well as Skyrim.
I also spend my time living and breathing, and drinking that sweet glass of life.
I write poetry, lots of it, check out my dA if that's your thing.