The subject behavior will occur if you installed a program that attempts to prevent the computer from turning off the display, or from entering standby, or from hibernating. Some backup applications, and CD / DVD burning software will try to do this. If you force the computer to standby or hibernate while one of these programs are running, the display may not turn on.
To workaround this behavior, restart your computer:
1. Press CTRL+ESC.
2. Press U.
3. Press R.
4. Press Enter