Do you mean the User's Interface? where you see your household members, their wishes, the options menu (a.k.a. "the ... button") and all that? If that's what you mean, try hitting the Tab or the F10 key a few times, those keys hide the user's interface and you might have pressed them by mistake. I doubt it is so if you say this happend inmediatly after loading the game, but still, it won't hurt.
If that doesn't help you should check your Saves folder (My Documents/Electronic Arts/The Sims 3/Saves) and see if the file is corrupted. If it is, it will end in ".bad" instead of ".sims3". Then you will have to go back to a previous save, as explained here:
http://www.carls-sims-3-guide.com/forum/index.php/topic,6.0.html. You will lose some progress depending on how often you save the game, but I think Metro will allow it
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If you don't have a .bad file in the saves folder, you can try reseting the world ("resetSim *" without quotes) and then hit alt+F4 to be prompted to save the game, and then exit. Make sure you back up first though!! just in case. I haven't tried this myself but I have read about it in the official forums and in other forums as well, so you can try.
Hope this helps! If you weren't talking about the User's Interface, could you explain it better? I just thought I would explain this here anyways to save you time in case that was actually the issue
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