Since starting to run Windows 8.1 a couple of weeks ago I have been unable to open iTunes, Getting the messages. 'The program can't start because MediaToolbox.dll is missing form your computer. Try reinstalling the program to fix this problem' & 'iTunes was not installed properly. Please reinstall iTunes. Error 7 (Windows error 126)'.

When I try to uninstall iTunes I get this message 'The feature you are trying to use is on a network resource that is unavailable. Click OK to to try again or enter an alternate path to a folder containing the installation package 'iTunes6464.msi in the box below'

I have no idea what to do to resolve either problem. I'm not very technical so very simple language would be greatly appreciated.