Login screens won't load

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Hi, guys. Ran into a weird, new problem after having my videocard replaced. I'm unable to open any login screen on my computer (Compaq Presario PC) at all, in any webbrowser. I keep getting error messages that my computer can not connect to the webpage (I tried many different sites that require logging in on a separate page.) I have cookies enabled. I've tried turning my firewall off, but that doesn't help either. Neither does clearing out all my personal data/cache/temp files.

So I've run out of my normal "quick fixes." Got any other suggestions or know how to help me?

Thanks, everyone!
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