Yamaha PSR S 650 Problem

by volan
(sri lanka)

once i noticed about pitch bend's error, i just took it to yamaha work shop & got it repaired. it was the only mistake it was having.

now the problem is when i connect USB pen it shows that " USB connecting" but doesn't display MIDI files, STY files, User Expansion file"
solution is only to restore factory setting or reset the system, how to do it step by step?

thanks