PLEASE help me!

I can't access to two university websites. It's been around 5 weeks since it stopped working.

Any other website works besides these two. No matter where I go these two websites don't work.

It says that safari can't establish a secure connection to the server. It doesn't work with firefox or chrome.

I tried erasing all the cache, the DNS thing, and all the solutions that were suggested online.

How can I fix this problem? Please Help me!