The popular, robust and free VLC Media Player has, like other media players, a repeat mode: a setting that endlessly loops a file or playlist. VLC's "Repeat One" and "Repeat All" modes are both activated via the same button on the VLC control panel, which is visible, provided the player's interface isn't set to "Minimal View."
Find VLC's Loop button toward the far right of the set of controls and marked with two arrows forming a loop. If you don't see any controls at all, right-click in the VLC window, point to "View" and uncheck "Minimal View."
Click the Loop button once to activate "Repeat All" mode. When your VLC playlist finishes in this mode, it will automatically repeat from the beginning. Manage your playlist by clicking "View," then "Playlist" and adding whatever files you want.
Click the Loop button again to activate "Repeat One" mode, which will simply repeat whatever the current file is. If you're not using a playlist, the "Repeat One" and "Repeat All" modes will have the same effect.
Click the Loop button a third time to turn off "Repeat" mode.