To fix your 120MR MP3 player you'll need to reflash the firmware.
The firmware can be downloaded from http://forums.cnet.com/5208-7595_102-0.html?forumID=71&threadID=218044&start=165
(see post 175 - Matsui120MR.zip it's a 3mb download).
Download and unzip this file then run stupdaterapp.exe with player connected - it should find the player. Tick the Format box (after backing up any files you want off the player) and Reflash your firmware then the player should work fine. This firmware also has bonus of allowing playback of songs by artist or album (instructions included with the firmware) as newer version than installed on most of the players.
In the unlikely event of your player refusing to turn on after an update remove the battery and press/hold play while connecting and when asked for driver it's in directory you extracted firmware to. Reflashing again after selecting driver should fix it.
I've recently used this to repair a batch of 7 players (2gb 120MR and 1gb 110MR models) bought as faulty cheap on ebay.
Nigel
June 2007