Sony Walkman NWZ-E436F Volume up button mulfunction

for the first time after not use in months (last two months still working).

1. charging error. it sometimes charged sometimes not charged just like the cable had problem. never had this problem for years since 2009
2. the date became --/--/--. never happened once although years not use.
3. after fully charged, it's working. all the music files available & can be played. JUST the volume up malfunction. volume down is working. now I'm worried, volume has down to 14 after I pressed two three times when confirming the volume button malfunction. HELP.