Has anything changed in the meanwhile? New plugins, new OS version?...
You could run the installer again, see if any file nees to be fixed.
You could try and disable any plugin you might have added yourself. This can be managed from X-plane plugin menu.
If nothing works, you could also delete (or move for backup) your X-plane 10/output/preferences folder.
If you can't solve the issue, include your X-plane 10/log.txt file so that Laminar Research (I am not part of the staff) has as many details as possible about the issue.