I've had problems with iTunes for a very long time, to the point where I quit calling their tech support. I couldn't get a sample to play for more than 20 or 30 seconds even though they are 90. On a VERY rare occasion it would go the distance. Anyway, last week the sample would stall and the little window saying, "Loading URL" would come up mid screen and just hang there. I could only get it to go away by hitting ctrl+alt+delete and closing the program through task manager. Well, another 2 hours on the phone with no results. The level 2 tech was going to call me back the next day.
I decided to do a complete uninstall of iTunes. You can't do that with Windows, only through Revo uninstall since it will scan your computer after the uninstall for any additional files and folders left behind.
After the reinstall, iTunes worked flawlessly for the first time in 5 years. Even downloads finished in a second or two instead of the 15 or 20 seconds it used to take.
I have the licensed pro version of Revo uninstaller, but you can get the basic one free. Try it.