Can't open dropbox links in Safari or Chrome

I'm a member of a teaching community on facebook, and the teacher posts links to dropbox for the students to download and work on at home. I just purchased a new, reconditioned, iMac Retina 5K 27-inch 2017 version, running High Sierra 10.13.5 and can't get any of his links to open in a new tab or new window. The link just shows a blank white screen, in both Safari and Chrome. If I try to open Dropbox.com the page doesn't load properly and none of the images load, just text.

Safari is version 11.1.1 and Chrome is the latest version 67.0.33966.99.

Trying to do the same thing on my MacBook Pro Retina 2015 version (same OS, same browser versions) it works perfectly, the files open and I can download them, and dropbox opens just fine.

I don't have any extensions in Safari, I do have home security on the network, but dropbox is listed as a safe websites, and if that was the problem the MacBook on the same network couldn't open it either.

Any suggestions how I can open these links on my iMac please?