wont-open.com - for all things that won't open!
Itunes won't open itself.
Go to windows control panel -> add/remove programs -> select Itunes -> select change -> reinstall or repair Itunes
Go to windows control panel -> add/remove programs -> select Quicktime -> select change -> reinstall or repair Quicktime
Multiuser PC Itunes - User rights
Right click Itunes and select 'Runs as', select different user.
Virus scanner blocking Itunes
Your virus scanner might block Itunes access to hardware. Check virus scanner log for Itunes.
Firewall blocking Itunes
Your Firewall might block Itunes access to the internet. Check firewall log for Itunes.
Corrupted Itunes library
Create a new itunes library file.