Check the following.
- Restart the TV.
- Connect to another USB port.
- Format the USB device (make sure file formats and system are supported on TV).
- Try with another USB device.
- If the issue is still unresolved, reset to Factory settings.
- Press the HOME button on the remote.
- Select Settings.
- Select System Settings.
- Select Customer Support.
- Select Factory Settings.
- Select OK.
- The initial setup screen displays after completing this process.
- Be sure not to turn the TV off during this period (it takes about 30 seconds) or press any buttons.