Web browsers say certificates expired or not yet valid, even though the certificate is valid for today's date and system clock is accurate

I just formatted my computer and reinstalled Windows (Windows 7 Home Premium SP1), and when I try to visit certain websites (eg Wikipedia), the sites do not load. The sites fail to load in both Chrome and Internet Explorer.

In Chrome I get the error cert_date_invalid. When I manually check the security certificate, it says "The certificate has expired or not yet valid"; however, looking at the dates, the certificate appears to be valid for today's date (ie, the range of valid dates includes today), and the system clock is correct. Many other sites (eg Google) do work and the certificates show up as valid.

Windows Update gives me the error 80072EFE, which seems to be a connection error. I've tried restarting the computer.

It turns out that the root certificates were out of date, as suggested by the comments. I downloaded the Windows update "Support for urgent Trusted Root updates for Windows Root Certificate Program in Windows" directly from the Microsoft site, which fixed the problem.