I was able to finally FINALLY FINALLY fix the problem. Yes, I tried all of the TLS and SSL check marks and unchecks.
Automatic updates review
Restore points
Different browsers (FireFox, IE, Edge, Chrome)
Resetting TCP/IP
Resetting Winsock
Clearing Browser History
Changing DNS settings
Testing TLS/SSL Browser settings on other sites confirmed all ok
Looked at the CERT, noticed it does not cover the domain WITHOUT the WWW but didn't make a difference and imported the CERT as well. For example...
https://domainnamehere.com instead of https://www.domainnamehere.com where the cert only covered other variances but not without the WWW but didn't make a difference.
Yes, tried the IP address directly avoiding DNS
Scanned for viruses
Downloaded Malwarebytes just in case and ran another full scan and scanned for rootkits
Cleared DNS cache, pinged DNS name, confirmed IP was correct, confirmed DNS had the correct entry
...and more, etc etc etc...
I was getting a bit frustrated and this is a fairly new install of Windows 10 just 3 weeks ago for a client and I absolutely did not want to start all over again so I troubleshot this for HOURS and took on HOURS more unbillable as I felt sorry for the client.
The workaround is using TOR. I used a TOR browser and I connected fine. Curiosity kicked in and I continued to troubleshoot....it was the antivirus. The same AV that has been running since day one. The same AV that ran on his Windows 7 PC prior to the Windows
10 migration. Accessing the same website as he always has for many years which is a government site required for his business. No idea why it just stopped all of a sudden but once I disabled the antivirus software, it started working.
Sergio Caro del Castillo
Cybershield
“If you think technology can solve your security problems, then you don’t understand the problems and you don’t understand the technology.”
– Bruce Schneier
Yes... the antivirus software is the culprit in my case too... I have stopped the antivirus and everything seems to be working fine without any trace of issue.... Thanks a lot... : )