I tried them with and without suggested settings (using UACdefault settings) , but it didn't work, so I uninstalled them again , set UAC to Never notify again and tried installing them again,I selected the Suggested settings with UAC disabled and now ALL the thumbnails work, but the videos that have thumbnails now and before didn't, don't work, just audio, and some of them can't be played (not even audio)
I have thumbnails now but a lot of files don't work