As a first step, make sure your device has all the features required to play your files by consulting the list of supported formats on our website www.archos.com.
With some ARCHOS devices, you may also need to buy an additional plug-in that lets you decode rarer formats that are not supported by default. This requirement will be announced by a message when you attempt to open the file. You can buy these plug-ins on either from Google Play or the archos online store depending on the device