Hi Jacek,
I'm not sure why your connection would suddenly stop working if it has been OK up to now, but if I were you I think I'd try and 'pair' your headphones with your Walkman again.
Start with the Walkman - on the 'home' screen select Bluetooth (the top right icon) and then select the 'pairing' option (the blue light on the corner of the Walkman should start flashing rapidly). Then on the headphones (I assume these are the ones that came with your Walkman (DR-BT21G)), starting with them switched off, press and hold down the round power button to first switch them on, but continue to hold down the power switch beyond this point until the red and blue lights flash repeatedly together (it should take about 10 seconds of holding down the power button the reach this point). The model number of the headphones should appear on the screen - select it by pressing the play button and then enter a passkey of 0000 (four zeroes), and press the play button again - that should be it!
One further thing you could do - on the home menu, go to 'settings' (the bottom left icon), and then select 'Bluetooth Settings' and select 'Quick Connection' - make sure that the model number of your headphones is highlighted - that way, next time you can connect your headphones with your Walkman by pressing and holding down the Bluetooth button on the side of your Walkman.
Hope this all helps - good luck!
