sharepoint server – The website can not be found

After disconnecting and attaching the content database with the message "Site error can not be found" in and in Chrome:

HTTP / 1.1 200 OK
Server: Microsoft IIS / 8.5
Date: Mon 27.7.2015 06:56:52 GMT
Connection: close

And in the log:

Category: Site Orphan
Error: That's right
UpgradeBlocking: False
Message: Database [WSS_Content_DBONE] contains a site (Id = 
                  [798c2f51-4e9e-44bf-bfad-c774a7b563d0]Url = [/]) whose id
is already assigned to another database (Id = 
                  [3637a130-6cf9-4932-8b9c-d85a7030c010]name = 
                  [WSS_Content_DBTWO]) in the sitemap. Consider deleting one
of these sites, which have conflicting IDs.
Remedy: The orphaned websites can lead to errors during the upgrade. Try to lose weight
and re-insert the database containing the orphaned sites.
If necessary, restart the upgrade.