Crikey. Okay, at least we've worked out that Apple Mobile Device Support definitely seems to have gone silly on the PC.
Let's try doing a "standalone" reinstall of AMDS.
Download and save a copy of the iTunesSetup.exe (or iTunes64setup.exe) installer file to your hard drive:
http://www.apple.com/itunes/download/
Download and install the free trial version of WinRAR:
http://www.rarlab.com/
Right-click the iTunesSetup.exe (or iTunes64Setup.exe), and select "Extract to iTunesSetup" (or "Extract to iTunes64Setup"). WinRAR will expand the contents of the file into a folder called "iTunesSetup" (or "iTunes64Setup").
Go into the folder and doubleclick the AppleMobileDeviceSupport.msi to do a standalone AMDS install.
(If it offers you the choice to remove or repair, choose "Remove", and if the uninstall goes through successfully, see if you can reinstall by doubleclicking the AppleMobileDeviceSupport.msi again.)
Does it install (or uninstall and then reinstall) properly for you? If so, restart the PC and check to see if ituneshelper is behaving itself again.
If instead you get an error message during the install (or uninstall), let us know what it says. (Precise text, please.)