Thanks. Yeah, I've rebooted both modem and router several times in the last few days and redone the router setup each time. The sites I'm unable to access are big ones, like Bank of America or ShieldsUp--sites that I'm sure are still active. All to say that to reinstall my PPOE software, check that the sites will open, then uninstall the software and do the router setup again is a bit of a pain.
But it DOES sound strange that some 90% of the pages I regularly access open with no problem, but a few won't.