In your main PC, open Internet Explorer, go into tools, internet options, advanced tab, and make sure that "use SSL 2.0" and "use SSL 3.0" are checked. Hopefully it works. You can google that error code if it doesn't.
Now, with the other problem with the router, I'm not sure what your set up looks like. It is difficult for others to attempt to diagnose the symptom. Are all three computers plugged into the router, then the router to broadband internet? Or, is your main PC connected via phone modem giving your other computers internet access through your ethernet port? Please be more specific.