If it works on a different PC, 2 steps I can think of:
1st, go to Control Panel, Uninstall a Program, and uninstall everything related to Apple such as iTunes, iCloud/Cloud and Bonjour.
Reboot then download them again and see if this solves it.
2nd, I had a similar case when Windows registry was badly damaged and I had to format the disk and do a clean install. That solved it.