Hello,
First of all, check whether search service is working. Go to Computer Management > Services and Applications > Services > Windows Search. This service should be running and use the Automatic or Automatic (Delayed Start) startup type. Then look for search settings: Settings > Privacy & security > Searching Windows. Look which locations are included to search, Classic may be the most safe option, Enhanced requires more time for building the index. Check the excluded folders here as well.
If the service is running and settings are OK, try to use search boxes in different places: in Settings, in Explorer, in Start menu. Check if it works at least somewhere or doesn't work at all. In the last case, try to use the troubleshooter: Settings > Privacy & security > Searching Windows > Indexer troubleshooter.