All the Windows PCs on my network this morning, regardless of version of Windows receive an ERR_CONNECTION_TIMED_OUT when trying to access www.dropbox.com. The OSX machines are fine. All receive IP (Address, DNS) info from DHCP server, all use same firewall that has no rules blocking outbound connections. I tried using Google DNS servers, same result. Does not seem to be a DNS issue as a ping to Dropbox from those PCs return the IP address correctly.
It is obviously something on my network, but why only the Windows machines?