"The certificate is not trusted because no issuer chain was provided" error in all browsers for all websites.

Question

As it says, Chrome, Firefox, and Internet Explorer all give the certificate error message for any and every website attempted - including the Firefox add-ons page. The specific error is the "no issuer chain was provided".
1) This problem is not on my computer - it is on my mother's computer in another city. Therefore, I cannot attempt every little possibility without flying over there - I'm looking for things I can tell her to do over the phone. The problem started today. I've already given her the list of anti-malware programs to go install and run from here:
https://support.mozilla.org/en-US/questions/982393
Note that, of course, she will have to accept the security certificate override to get to these things - I hope this isn't bad.
2) The problem started after she tried to use Skype, it hung for a very long time and would never log on. So she tried to reinstall it - and she said she clicked through a number of agreement screens and believes she may have installed malicious 3rd party software. This is ridiculous, is Skype now putting malware on people's computers through these bogus 3rd party add-ons at installation? I suppose it is possible Skype was hanging because of some other problem - but she did manage to reinstall Skype and got it to work (but now her internet certificates won't).
3) She has BitDefender. I am aware that it says here:
https://support.mozilla.org/en-US/kb/connection-untrusted-error-message
that she should turn off SSL scanning. She turned it off, it did not solve the problem. She turned it off and restarted, it did not solve the problem. She has had it on for the past 6 months and it has never caused a problem.
4) In addition, BitDefender reported today that it stopped a malicious program called MySearchDial.exe from attempting something it shouldn't. We went through this removal guide:
http://malwaretips.com/blogs/start-mysearchdial-removal/
however, the software MySearchDial was never actually installed into the windows install list, and we did not find any addons/plugins in any of the browser lists (note that Firefox add-ons cannot be accessed with a certificate error, it gives the error message but DOES NOT give you the option to add an exception so you can't access the add-ons). The only thing we found was (a) MySearchDial was default in the IE search engine list, despite there being no add-on, and (b) MySearchDial.exe was in the temp folder (now deleted). I note that I had BitDefender scan the temp folder *before* I deleted MySearchDial.exe, and it claimed no threats were found. What? It was BitDefender that warned me of it in the first place!
5) Time and date are correct.
6) Checked the Win 7 install log, only Skype, Skype Click-to-Call, and (for some reason) Mircosoft Visual Studio 2010 and Visual C++ were installed or altered today. I got paranoid about Click-to-call and asked her to uninstall it, but it didn't solve the problem.
7) The OS is Win7 64bit Home.
Anything beyond endless Malware removal programs (via list linked above) that we should try?

Answer 1

The only way to know what is going on is to retrieve the certificate and check who is the issuer.<br />
It is always possible that the server doesn't send the full certificate chain (intermediate certificates), so it might help to post a link to this website
Check the date and time in the clock on your computer: (double) click the clock icon on the Windows Taskbar.
Check out why the site is untrusted and click "Technical Details to expand this section.<br>If the certificate is not trusted because no issuer chain was provided (sec_error_unknown_issuer) then see if you can install this intermediate certificate from another source.
You can retrieve the certificate and check details like who issued certificates and expiration dates of certificates.
*Click the link at the bottom of the error page: "I Understand the Risks"
Let Firefox retrieve the certificate: "Add Exception" -> "Get Certificate".
*Click the "View..." button and inspect the certificate and check who is the issuer of the certificate.
You can see more Details like intermediate certificates that are used in the Details pane.
If "I Understand the Risks" is missing then this page may be opened in an (i)frame and in that case try the right-click context menu and use "This Frame: Open Frame in New Tab".
*Note that some firewalls monitor (secure) connections and that programs like Sendori or FiddlerRoot can intercept connections and send their own certificate instead of the website's certificate.
*Note that it is not recommended to add a permanent exception in cases like this, so only use it to inspect the certificate.