1. Start > Run > Notepad.

2. Paste the following:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MediaPlayer\PlayerUpgrade]
"AskMeAgain"="no"

3. Save it as disableupdatemessage.reg

4. Double click the file, it will ask you if you want to add the information, select yes.