Well if you have taken a troubled system direct to the net rather than going through it's current connection with no change then I am at a loss, to get the same issue on more than one system is freaky, unless they are blocked at the source, but taking a system direct to the net rather than through it's current configuration should rule out any issue with the router blocking it I'd of thought.
TBH this is getting out of my depth here, it is an area where I would stumble around trying to provoke reactions\clues as to what may be gong on, but as I can't see what you see I may miss some slight thing that may offer such a clue, so you will need to keep your eyes open and use common sense with what you see then hopefully we can find a cure to this.
Now I can only think of 2 things that could be affecting this, thats an infection, or a firewall in some shape or form, the fact it's more than 1 PC suggests it's more likely some kind of firewall issue, but it doesn't mean infection can be ruled out, so out of interest have you run any scans at all ?
The settings for the router(s) or on the PC to connect to them is the more likely problem, and this is where I start to stumble around, so I hope I can be clear enough for you to follow here.
Lets start with the simplest setting, right click on the connection icon (the TV's flashing by the clock) and select Open Network Connections, this will open a window which will list ALL your connection points, so there could be 3 or 4 devices listed depending on your set up, right click on each icon (one at a time) and select properties, I suggest starting with the one currently connected which should be obvious when you see them as thats the problem one, with the properties window open scroll down (if needed) until you see Internet Protocol (TCP/IP), now double click on that to open it's settings, there are 2 halves, in the top half make sure Obtain IP Address Automatically is checked, and while we are there I would set the bottom half to the following DNS servers, it will be a security blanket that stops you accessing known bad sites (the serious ones), so under Preferred DNS server enter 208-67-222-222, now against Alternate DNS server enter 208-67-220-220 and OK\exit from that, now repeat with each other connection listed (not the 1394 one if you have that showing).
Try the connection now, more so if the settings were other than what I have mentioned here, but not sure about clearing cache or anything if that may be required to clear the old settings, as I say I am a little out of my depth here, another quick and easy test, follow the previous advice to reset the security zones, but this time don't touch the default button, instead highlight the Trusted Sites (a green check mark icon) and click on Sites which will become click-able after the icon is highlighted, in there type one of the problem sites (eg Walmart) address into the box, uncheck the Require Server Authentication at the bottom then click Add, if you don't uncheck the box it will not accept the site unless it is an HTTPS site, save\exit and try going to that site, see what happens there.
Are you running a software firewall ?
Can't hurt to have a look through that to see if anything is blocked, a more extreme option is to hard reset the router(s) to factory state, but you will need to be aware of any settings you may need, user name\password and the like, in my experience it normally doesn't need this, but not know your specific connection I can't be sure if there is a freak issue I don't know about, so if in doubt don't do this, we need to keep you with a connection to try and get this sorted, but if your comfortable to try then in each router you will find a small pin hole type thing, using a Biro or similar unplug from the mains then press and hold this button for 30 seconds or so, now power it up again and see what that brings.
Try these suggestions and report back with the results, the next step if required will be logging into the router(s) directly and checking out the settings in there, but I am hoping something within this will help, good luck.