Hi Nigel,
I have just experienced the same problem, luckily for me though it was the first time I let the battery completely discharge (not for too long a period though) and using the reset button did work and I am now able to recharge the Walkman.
On looking at the Sony website "problem resolving" page for this model it suggested that you may need to take it to a Sony dealer and have the battery changed as the battery may be too old and not be rechargable any more.
I hope this is of help
Regards
Tony W
