Hey, as long as this is turning into a PC Tech suggestion thread, here's mine...
Do what they suggest, eliminate all connection points between the PC and cable modem, and ipconfig /flushdns and ipconfig /registerdns again. Check that there are no other servers but localhost with ipconfig /displaydns.
Then, hop on up to
www.grc.com and run his Shields Up! profiler. It's horribly enlightening and scarey (not that you are affected, but you never know). Do this with and without your router.
The only other thing that I can imagine is something is intercepting the DNS lookups. Can you hard-code your ISP DNS servers on the connection profile?
I've honestly never heard of this - and I've run virusscanner/adware free for 10 years on the internet, and never been infected. Strange that so many people are.