Internet Security EXPERTS, what is this?

I had only my gmail account open and I think my Yahoo one as well. I was basically typing on a Microsoft Works new sheet and was not sending or receiving emails. I don't if I pressed a key somewhere,, but suddenly I started getting this message:

REVOCATION INFORMATION ABOUT THE SECURITY CERTIFICATE FOR THIS SITE IS NOT AVAILABLE. DO YOU WANT TO PROCEED?

When I clicked NO, I got the following:

THIS CERTIFICATE CANNOT BE VERIFIED UP TO A TRUSTED CERTIFICATION AUTHORITY

ISSUED TO: gateway.2wire.net

ISSUED BY: GATEWAY AUTHENTICATION

VALID FROM: 1/16/2007 TO 2/11/2022

I wasn't going to include the name of company nor dates for security reasons, though I know nothing related to security or such, but I do hear of comp. being hacked all the time and viruses and whatever else. But I feel that by providing all this information I can get some help from Yahoo experts.

Whether I kept clicking YES I want to proceed or NOT, I would get further messages warning me. I didn't copy and paste those. But it just kept popping up as I proceeded to sign out of my Yahoo and my Gmail account. Basically every time I would close a page, I guess. And then a screen popped up and I got this message sprawled on entire page:

There is a problem with this website's security certificate.
The security certificate presented by this website was not issued by a trusted certificate authority.
Security certificate problems may indicate an attempt to fool you or intercept any data you send to the server.
We recommend that you close this webpage and do not continue to this website.
Click here to close this webpage.
Continue to this website (not recommended).
 More information

If you arrived at this page by clicking a link, check the website address in the address bar to be sure that it is the address you were expecting. When going to a website with an address such as https://example.com, try adding the 'www' to the address, https://www.example.com.
For more information, see "Certificate Errors" in Internet Explorer Help.

IS SOMEONE TRYING TO GET MY INFORMATION OR HACK INTO MY COMPUTER FOR OTHER REASONS? PLEASE HELP ME!
The security certificate on the site has probably expired. It should be nothing to worry about, just make sure you have an anti-virus program installed for any possible future risks.