Before I wrote the first post, I restarted both computers that wouldn't load gmail. After seeing Mac's latest post, I tried it out before rebooting. gmail came right up.
Whatever it was had a time component, which makes me think it was neither my computer(s) nor modem/router.
A good answer is easier with a clear question giving the make and model of everything. "The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
