Express Plugin does not show up in PowerPoint after install.

First, make sure that the plugin is compatible with your computer. You need to be on a PC running Windows XP or newer and have Office 2007 or newer.
If you meet those requirements, try uninstalling the plugin using the Windows Add/Remove Programs wizard.
Open Add or Remove Programs from Windows and find Express Plugin for PowerPoint and uninstall it.
Next, reboot the computer.
When you log back into the computer, try running the express plugin installer again and keep the default installer settings. You can find a download link for the latest versions here.
If the plugin still does not show up in PowerPoint, maybe there is a prerequisite that is not installing properly.
First, please uninstall Express Plugin just like before.
Then manually download and install 2 packages directly from Microsoft's support website. Download both of them one at a time and run the installers.
The first is called VSTO runtime for Office. In almost all cases, it's already on your computer, but if there is a problem with it, this installer will fix it.
The next one is called the 2010 Primary Interop Assemblies (2010 PIA).
After installing both of those, restart the computer and then install Express Plugin again.