Can any one help?Dead mp4 player 2gb nano clone.

PLEASE!
Can someone help...have been selling 50 of these and they have been great,except 3 have died - were working fine,and not messed with firmware upgrade,but now just nothing when switched on[charged].Am on behalf of those who bought them.Any help will be MUCH appreciated!!!!!!Thanks.

Hi I am baljit I have mp4 player of wilson company limited
Version : 3.4.37
I have upgrade firmware of player with version 3.5.37 and after
upgrading my player is doing nothing. However it connect with
pc as disk drive but it never play audio and video songs.only blue
screen is appear. So please tell me how I can recover player and
send me Firmware of following version at
my e-mail: baljitbelli@yahoo.com
Device: S1 mp3 player
Producer: Wilson Co.LTd
Version: 3.4.37
Thanks

my mp4 player is frozen on a blue screen with an hour glass and i tried the hold button and then i tried holding the center and top button plzz help i just got it. thanks for your time