Sony's Walkman range of MP3 and mini-disc players update the 1980s brand for modern digital technology. One feature common to many models is the "Hold" switch, which disables the controls to prevent buttons from being accidentally depressed.
Locate the "Hold" switch on the body of your Walkman. It is typically small and minimally marked, and located on the side or bottom. It is usually a small sliding knob set into a recessed channel with the word "hold" or "lock" printed at one end.
Set the switch to "Off" by sliding it to the left.
Set the "Hold" switch on the headphone adaptor to "Off" by sliding it to the left. If your Walkman does not use a headphone adaptor, this step is not necessary.
If your Walkman still does not play after both "Hold" switches have been disabled, reset the unit and check that the batteries are fresh and that the storage card, if any, is correctly inserted.