Suggestion. Turn off file sharing, delete the preferences file for it and then restart. If the preferences file is garbled OS X may not be able to start up file sharing.
Having said that, I confess I don't know which file to delete. There is a SharingPref.prefpane in the System folder Library folder. If you want to try this one just move it to a safe place then restart. If it was a necessary file you can then move it back.
Please take this as a suggestion, not as gospel. I don't have experience in OS X deleting prefpanes and having the system recreate them.
Another place to get information like this is Apple's site. Click Support then discussion then OS X.