I will guess these radios will be treated like so much other electronic equipment, throw all and replace. However, before you do that, see if you can locate the fuse for the radio, and pull it. Leave it out for at least 30 minutes or more. Replace the fuse and see if the radio has "reset".
Also, I entered your question "Hyundai Radio preset buttons are not working" into Google and found several results that might help, including a reset procedure.
Hope this helps.
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Pennsylvania, for 60+ years, most recently, Allentown, now TV. 
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