Mavericks offers a lot less resolution options in the “Scaled” list than 10.8 or earlier did. This can be a particularly severe problem if the resolutions that it thinks your projector supports are not, in fact, supported by it at all, as was the case with my setup.The fix for showing the extended list of possible resolutions in Mavericks is undocumented, so far as I can find, but incredibly easy:

In the Displays preference pane, hold down the option key and click the “Scaled” radio button. This will toggle on and off additional resolutions for the device (including more scaled resolutions for the built-in display in MacBooks).

I’m not aware of any radio button ever having worked that way before, so it’s easy to miss.

If your external display isn’t showing an image at all because the OS got its “native” resolution wrong, you will of course have to click the “Gather Windows” button at the bottom of the preference pane to bring the w …

Source: Mac OSX Hints