Extensions are opening, but they are greyed out

If those are extensions you downloaded from the Internet (e.g. GitHub) your problem could be related to your version of CSXS. Unsigned extensions will only run in Premiere if you set Premiere to developer mode, and you need to do that for each version of CSXS running on your system. So if your Premiere came with a new CSXS version you will need to repeat what you have done when you first installed your extensions (if you can't remember you will a description in the installation process for an extension I developed here: http://markerbox.pro/installation).

If it's not that it could also be the file manifest.xml in the CSXS folder of your extension. Open it with a text editor and check whether the required versions of Premiere and CSXS match your system. Sometimes developers exclude newer versions of Premiere or CSXS, although the extension may work without a problem. Simply change the versions to your versions, save the file, restart Premiere and see whether the extension works.

If both attempts to fix your problem don't work the blank window could be related to programming issues in the actual HTML or Javascript of the extension. But that's where it starts getting complicated.

Good luck!