Mac or Windows, and EXACTLY which version of the operating system?
Recent Mac AND Windows operating systems have been known to cause "odd" problems
Are you using a computer Administrator account will full read/write permission?
Please read https://forums.adobe.com/thread/1499014
-try some steps such as changing browsers and turning off your firewall
-also flush your browser cache so you are starting with a fresh browser
-check hosts file for blocked entries https://forums.adobe.com/thread/1912777