Hi folks,
after 4 days of hard job, finally i've found how eliminate this problem even if your pc has one account NOT infected. This because the malware (not recognized) only affect the user is on line at moment of infection.

This procedure has deleted the problem:

1) Logon with user that has not affected by the problem

2) type "regedit" in Run window

3) locate [HKEY_CURRENT_USER\Software\Microsoft\MediaPlayer]

4) Export that section as filename.reg

5) edit with NOTEPAD this file and replace any string that's containing last username with your! (ex: c:\document & settings\anne\document --->> c:\document & settings\Max\document)
Save the file

5) Logoff

6) Logon with the user affected by the problem

7) type "regedit" in Run window

7)locate [HKEY_CURRENT_USER\Software\Microsoft\MediaPlayer]

8) delete it!

9) close regedit

10) locate the file you've modified, click with right mouse and choose "Merge".

That's all, now you can play all your MP3!

I'm sorry about my poor english
Max