I transferred many .avi files to my external (windows) hard drive and plugged it into the ATV but I cannot find them. Where are they located in the ATV menu? Thanks!
Hopefully your external drive is not NTFS. If it is, OS X can not read NTFS without special software installed and I don’t think it is Apple TV compatible. If the drive is FAT32 then you should see if in the Movies folder under a shortcut with the same name as the drive.