Check that you have a link to your plugin file in the appropriate Photoshop plugin folder.
Photoshop CC 2018, 2019, 2020 - C:\Program Files\Common Files\Adobe\Plug-ins\CC\
Photoshop CC 2015.5 - C:\Program Files\Common Files\Adobe\Plug-ins\CC\
Photoshop CC 2015 - C:\Program Files\Adobe\Adobe Photoshop CC 2015\Plug-ins\
Photoshop CC 2014 - C:\Program Files\Adobe\Adobe Photoshop CC 2014\Plug-ins\
Photoshop CC (2013) - C:\Program Files\Adobe\Adobe Photoshop CC\Plug-ins\
Photoshop Cs6 - C:\Program Files\Adobe\Adobe Photoshop CS6 (64 Bit)\Plug-ins
This folder will be full of Windows shortcuts that point to your Topaz Labs plugin file.
This folder should look something like this:
The little arrows on the folder icon indicate that this is a Windows shortcut.
If you right-click on one of those links and choose "Open Folder Location",
you will be taken to where your Topaz Labs plugin files are. For example for Topaz Labs DeNoise AI, selecting "Ope Folder location" will take you to "C:\Program Files\Topaz Labs\Topaz DeNoise AI" or "C:\Program Files\Topaz Labs LLC\Topaz DeNoise AI" if you have version 2.0 or later.
where you will see two folders, PS_Plugins, and PS_Plugins_x64
If you are using 32 bit Photoshop your plugin file will be in the PS_Plugins folder.
If you are using 64 bit Photoshop, your plugin file will be in the PS_Plugins_x64 folder.
Going into that folder you will see a file something like this:
It is a file with a .8bf file extension. That is the plugin file that will open your Topaz Labs photography software when you invoke it as a plugin from Photoshop. If that file is not there, your plugin will not work.
If any of these things are missing, please run your Topaz Labs installer without any other programs running and verify that these files have been installed correctly before opening and running Photoshop again to test your plugin.
If you can confirm that these files are there and your plugin still does not work, it is possible that these files have become corrupted. Please delete the link file in your Photoshop plugins folder eg. "C:\Program Files\Common Files\Adobe\Plug-Ins\CC"
and run your Topaz Labs installer again from start to finish with no other applications open. Please contact Tech Support if you still cannot get your plugins working for you in Photoshop.
Thanks to Lance Hill for informing us the plugin folder for CS6