Hi, just seen your post and your frustration met mine. I tried everything like you and eventually gave up and was considering re-installing Windows 7 to see if that would solve the problem.
However, before doing that, I started having problems with another programme, Adobe Premiere Elements (video editor), which also started refusing to open up. I de-installed the programme and re-installed but that didn't work, so now I had 2 programmes which wouldn't open - Itunes and Adobe Premier Elements.
And then another programme started to take ages to get going and this was Autologics Defrag Utility. I de-installed and re-installed but that didn't work. This defrag utility was taking a very long time to find disks to defrag - about five minutes.
I only have 2 disks in my computer (C) (D) but the Autologics Defrag Utility was looking for and found four other 'devices with removable storage' named (H) (J) (L) (F) which didn't exist. I googled this and found advice that said I could disable these devices (USBs) - which I did. AND LO AND BEHOLD all the programmes which weren't working, suddenly, almost miraculously, started working as they should. Why I know not! Itunes and Adobe open instantly now. In fact the computer is behaving like a new machine.
It seems to me that there may be a variety of reasons why some programmes start behaving badly - finding the answer, in my case, was plainly accidental.