Some times in Open office or Libre office by default spell checking is not enabled.
How to enable spell checking :
Open openOffice/libreOffice writer, go to Tools –> Options –> Language Settings, it looks similar to below image.
In language setting tab go to Default language settings where select Western value as the language for which you want to enable spell checking.
In above image the language I amusing is English (USA), and you can view a blue write mark beside English (USA) that means spell checking is enabled for the language English (USA). If there is no blue mark the spell checking wont work.
After updating settings, restart the office document that will enable spell checking.