If you've got a Linux host with VMware installed, periodically you may notice your Control, Alt, and Shift keys stop working in the host operating system, but still work in the virtualized OS, regardless of what it is.
This is caused by what appears to be a bug in VMware Server, and possibly other VMware products. Control-Alt is the default combination to return from a VMware virtualized guest OS to the host OS, if VMware tools are not installed on the guest. It appears these keys are still trapped by VMware, even though the focus is on the host OS.
Restarting the X11 GUI will fix the problem, but this is annoying, as it usually means a logout, or at least shutting down active applications.
However, typing "setxkbmap" in a console window will also usually fix the problem, without the need to restart X11. This can also be added to the desktop as a shortcut, or the menu, so you don't need a console window open.
In the odd case where this may not work, using instead "setxkbmap us -print | xkbcomp - $DISPLAY" should fix it. This one, obviously, needs to be a shortcut, as you can't type the capital letters you need without a shift key.