Q: Updated to Itunes 12.1 now it wont open, even after re install. Any suggestions?

Hello, SombreroMonkey.  

Thank you for visiting Apple Support Communities.  

I understand that iTunes quits unexpectedly.  Here is the troubleshooting article that I would recommend going through for this specific issue.    

iTunes for Windows Vista, Windows 7, or Windows 8: Fix unexpected quits or launch issues

http://support.apple.com/en-us/HT203206

Cheers,

Jason H.