I was not using my Sony walkman for last 3 months.
After keeping it idle for three months, finally one fine morning I pick it up for my exercise regime (which I was planning for the last 6 Yrs), to find out it was not working.
I think the battery discharged beyond its safe limit. As every cell requires a minimum residual charge to pickup the charge. Even though it was not switching on, transferring of files to the device or upgrading the software was not an issue, as it was getting detected on computer.
I searched internet for opening procedure of the device for disassembling it, as I could not find any screws or locking mechanism. After trying all the method and staring the device a lot, I got frustrated and break open it.
The green stuff sticking outside is the battery.
Remove the pink panel as shown in the image (marked with red circle). There are two small screws (circled in red colour on the walkman). The pink panel is fixed on the walkman with adhesive. remove it using a thin screw driver.
Remove the second panel as shown in the image.
All the four screws are marked with red circles. and both panels are also shown in the image. After removing the screws, walkman can be easily opened.