Some video drivers register Ctrl+Alt-* shortcuts for their actions, thus preventing other applications from using these keys (ATI video drivers and Intel Extreme Graphics are known to cause this). It can be also some other application.

The solution is to either locate the application that takes over these keys and shut it down or assign different key combinations for actions which do not work in Settings | Keymap.

So, it's rather a system configuration issue, than IntelliJ IDEA problem.