Microsoft Office Mac 2011- Can’t do spelling and grammar check on existing word doc

I have installed Microsoft office mac 2011 on my apple laptop last year. Yesterday, when I tried to open an existing word doc and try to do a spelling and grammar check it says "Word cannot start the spelling check. The spelling checker files may be missing. Make sure the spelling checker file are installed or use the Microsoft office Installer to install the spelling checker." I can't exit out after this pop up appears the only way to exit is to force quit on my apple computer. 

Please let know why this is happening and how I can possibly fix it. 

Thanks!