what do you mean by the icon dissapeared?
did you check your control panel, programs?
Can you find it there?
You said you tried to uninstall it and re-installing it again, what errors did you encounter when re-installing the itunes application?
Do you have any problem downloading the itunes from the apple website?
Did you try registering again with another email?
Can you confirm that you are logged in as administrator in windows?
ok i need you first to check that itunes in uninstalled completly
Go to Start > Control Panel
In Control Panel, click Uninstall a program.
Select iTunes from the list of currently installed programs; click Remove or Uninstall.
Then restart your computer
when you go back again go to programfiles right click on the itunes folder and delete.
Restart your computer
Install the version from www.apple.com
Can i just make sure of something, Do you have an antivirus installed?