Whether it’s the cat walking over the keyboard, the toddler pressing random keys, or simply the slip of a finger, the result can be part of Lightroom’s interface going missing. These are the most frequent mishaps:
The minimize/maximize/close buttons are gone!
If the window buttons at the top of the screen are missing, and you can no longer move the Lightroom window around, you’re in one of the full screen modes. Press Ctrl-Alt-F (Windows) / Cmd-Opt-F (Mac), or to go Window menu > Screen Mode > Normal.
Everything’s gone black!
If everything goes black apart from the photos, you’ve hit the L key and enabled Lights Out mode. Press the L key once or twice until everything reappears.
If there’s only one large photo filling the screen, you’re likely in Full Screen view. Press F or Escape to cancel.
The Done button is missing
If the toolbar under the photo, which contains the view mode buttons and sort order in the Library module, and the Done button in the Develop module (among other things) goes missing, then you’ve accidentally pressed the T key. Press it again to make the toolbar reappear.
My Filters are missing
If the filters at the top of the Grid view are missing, you’ve pressed the \ key. Press it again!
My panel is missing!
If a side panel goes missing, right-click on one of the other panel headers and check the panel name again, or go to Window menu > Panels and select the name of the missing panel.
There’s writing in the corner of my photo!
If the Info overlay is showing in the top left corner of the photo, press the I key once or twice to hide it.
There are red and blue marks all over my photo!
If there are red or blue patches on photos in the Develop module, you’ve turned on the clipping warnings. Press the J key to disable them.
My local adjustment pins are missing!
If you have the adjustment brush, graduated/radial filter or spot removal tool selected, and your existing adjustments aren’t displaying their pins, you’ve press the H key to hide them. Press it again to show them, or select Always or Auto in the Show Edit Pins pop-up in the toolbar.
My photo’s gone red
If you’re in a local adjustment tool (graduated filter, radial filter or adjustment brush) and the picture goes red, green, white or black, you’ve pressed the O key. Press the O key again to disable the mask overlay or toggle the checkbox in the toolbar.
These are the most frequent issues, because they’re all caused by a single keypress or the accidental click of a mouse, but if you have another issue you can’t figure out, you’re welcome to post a description and screenshot on the forum at http://www.lightroomforums.net.