I had the same problem on my Windows 8 machine. I had tried updating iTunes to 12.2 and the installation appeared stuck, so I canceled it. Little did I know that I would not easily open iTunes again. Downloaded the setup program and got the same message.
When the installer asked me if I wanted to undo the changes by that installation to continue, I clicked No. Then, I opened a Windows Explorer window and navigated to C:\Program Files\iTunes and double-clicked on iTunes.exe (the extension may be hidden), and the previous version of iTunes opened up just fine. I had it check for updates, and it found and installed the latest with no problem. iTunes is now displayed on my start screen, too. With any luck, this will work for you, too.