This could be the result of many causes like: improper firewall configuration, slow Internet connection, malware, background downloading, proxy configuration. For each of these cases you need to look for specific settings like:
Firewall configuration: Please check in Control Panel under Windows Firewall or System & Security. Disable the firewall and try again.
Slow Internet connection: You need to contact your ISP for more details.
Malware: Use an anti-malware solution to check for known Trojans and virus applications.
Background downloading: Sometimes updates are downloading in the background so you won't have to interrupt your work.
Proxy Configuration: Basing on the browser you are using, please navigate to Network, Connections and Proxy settings (Firefox, Internet explorer, Chrome) and uncheck everything it's related to proxies.