Ensure the card is formatted to FAT32 and the files are in MP3 format. The TDV26 generally supports cards up to 32GB.
Connect the included USB cable to the port on the speaker.
This usually indicates a low battery. Recharge the device.
Plug the 3.5mm audio cable into the "Line In" port. It acts as an external antenna; without it, reception will be poor. Press "M" until the screen shows a frequency (e.g., 87.5).
To change the volume, you must long-press the << (Volume Down) or >> (Volume Up) buttons. A short press will only change the track or station.