It's weird that your system will only play CDs if you turn the system off, then on again! So I can provide you with the most accurate information on this, can you please let me know which model of the 321 system you have? If you are unsure, you can double-check this using our Product Identifier.
One thing that would definitely be worth trying is a reset of the system. You can do this by disconnecting it from the power for at least 30 seconds, before plugging it back in and allowing it to boot back up.
I look forward to hearing back from you!
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