I tried following all of the troubleshooting steps for downloading the latest version of iTunes - still no success! I can't even get it to reinstall now.

See if the user tip: https://discussions.apple.com/docs/DOC-6562 doesn't help

I've just (finally) managed to fix this problem today. I checked the Apple Support forums, and it seems a lot of people are having the same problem.

I rang the Apple Support line, and the very helpful man (thanks Alan!) talked me through it stage by stage. If you go to the following page on the internet: http://support.apple.com/kb/TS5376 it takes you through the process. WARNING - it takes a little time! The main purpose of this is to remove any trace of the old version of iTunes from your computer...

Basically, the first thing you have to do is go to your Program Files and double click on your iTunes folder. There'll be a number of files with the suffix .dll - you need to move all the .dll files from that folder to your desktop - you can simply click and drag them on the desktop..

Next, uninstall iTunes - go to Control Panel / Add/Rempve Programs and when the list comes up remove iTunes. This will take a few minutes... Then reboot your computer.

Next, go back to Control Panel / Add Remove and Remove - IN THIS ORDER -

Apple Software Update

Apple Mobile Device Support

Bonjour

Apple Application Support

Reboot again!

Next, check in your Program Files that the iTunes folder is completely gone - if it has, great: if it hasn't, right-click on the folder and press Shift and Delete - it will say "Are you sure you want to completely remove the folder "iTunes"? Click on "Yes".

Reboot!

Then go to the iTunes download page and voila! It should download iTunes without any problems... well it did for me.... Good luck!