|Check Internet Options (from Control Panel or Internet Explorer Tools / Options /Connections Tab / LAN Settings and make sure Proxy Server is unchecked even if using Firefox. Check settings in Firefox in Tools / Options /Advanced Connections / Settings (should be either use system proxy settings or no proxy).|
Check for malware especially using malwarebytes.
Try these two commands in that order in an elevated command prompt. Do the first one first then reboot and try. If still bad try the second.
netsh winsock reset
netsh int ipv4 reset
If these don't help, please post the output of an ipconfig /all command