A possible cause is security software (firewall) that blocks or restricts Firefox without informing you about that, possibly after detecting changes (update) to the Firefox program.

Remove all rules for Firefox from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox.

See Server Not Found - Troubleshoot connection problems and Configure firewalls so that Firefox can access the Internet and http://kb.mozillazine.org/Firewalls

Firefox doesn't shut down cleanly. It never has. It often only does a "top kill" which leaves the bottom running. It won't start again until you kill the entire process. Open Task Manager, hunt around for the remnant of the application ("firefox.exe"), and kill it using a bottom kill.

(Excuse my oil well terminology :-)

iv tried both suggestions and nothing is working