Spell check does not work in my LIbreOffice. I hope someone can help me to solve the problem!
TIA! 
To help you, first help us to understand the issue. Edit the question to provide minimal information.
OS name, LO version.
What have you done? What kind of text have typed (how?)? Have you set the text language (eventually set it to “None”)? Is the spelling module installed?
Attach a sample file so that we can check if it is intrinsic to the file or related to your installation/configuration.