I cannot open iTunes on my computer!

The general troubleshooting advice when iTunes fails to install properly (and reinstalling or repairing it does not work) is to remove not only iTunes but all related components, reboot, remove the target installation folders and reinstall. See the Removing and reinstalling iTunes and other software components section in:

Troubleshooting issues with iTunes for Wi… - Apple Community

If it's the icon on the Taskbar, and it has turned white and is no longer working, that indicates that the shortcut is not found. This occurs after every update I make to iTunes.

However, if you opted to have the iTunes icon on your Desktop as well, that should still be working, as should the All Programmes/iTunes/iTunes option.

If the problem is only with the Taskbar icon, delete it (right-click/unpin from taskbar) and create a new shortcut, which can be achieved by either of the two following methods:

• • drag the Desktop icon to the Taskbar
  • go to the All Programmes/iTunes menu and then right-click the iTunes entry from the list, then the More option and finally Pin to taskbar:

That's All Programmes (1.) {- the Windows start icon}, then the iTunes folder and right-click iTunes (2.) from the list, then the More option and finally the Pin to taskbar option (3.).