If OSv3 or whatever is refusing to uninstall just use revo.
If you can't find the item installed in the application or other programs list hit forced uninstall icon and navigate to where ever you installed your previous version of OS.
In my case its:
Make sure you do an adcanced system scan to uncover any left over registery entries.
Once everything has been deleted restart. Re-install halo and OS 4.0 and report back.Edited by Super Flanker on Jun 25, 2016 at 02:15 PM