Starting with oC8 the windows support was dropped:
https://doc.owncloud.org/server/8.0/admin_manual/release_notes.html#windows-server-not-supported
Additional to this ownCloud 8.1 won't run at all as an "hard-fail" will be added:
The official blogpost about the dropped windows support is available here:
ownCloud Server 8.1 Will Not Support Windows as Server Platform Natively