PowerPoint freezes and shows a Downloading box every time I open PowerPoint

Express PowerPoint Plugin > Support Help

The downloading dialogue box is for a file connected to the Express plugin that is either missing or out of date. The Express plugin may not be able to establish a connection.

Close PowerPoint and go through the following steps to resolve the issue.
The Express plugin may be attempting to use a Proxy Server to connect even if there isn't one.
To fix this, you will need to manually download the database file that the express plugin is trying to download when PowerPoint starts, then change the settings.
    A. Download this file and save it to your desktop. http://www.presentationpro.com/downloads/PresPro_ExpressDB.zip 
    B. When the file is finished downloading, copy it to the following directory on your computer. 
        (if you can't find the folder "AppData" see below)
    C. Open the file and Extract the contents to this same folder. When this is done, you should have 2 files in the DB folder. PresPro.mdb and PresPro_ExpressDB.ZIP
    D. Open PowerPoint and it should now skip over the downloading message and load a blank presentation.
    E. Click on the PresentationPro Ribbon and click Search Designs to open the Express Plugin.
    F. Fill in the necessary fields to login.
        (If it is a trial account, only put your email address in and click Login at the bottom.)
        (If it a customer account, fill in your email address and password only and click the Login button at the bottom)
    G.Here’s the trick that fixes it…On the Welcome screen, fill in your email address and password. Then you need to check and then uncheck the proxy option. Put a check next to “Use a proxy server to connect” and then click it again to remove the check. The rest of the fields underneath should disappear. Click login at the bottom. 
    H. Click Search in the Express plugin to load designs and then try to apply a design and it should now be working.
How To Show the "AppData" Folder: 
If you are not able to find the AppData folder, windows has it hidden from view. In the Windows Explorer, click on Tools, Folder Options and go to the View tab. under Advanced settings, click the "Show hidden files, folders, and drives". click Apply and then OK and the AppData folder will show up.

Other possibilities

1. If you are using a VPN, temporarily disconnect from it and open PowerPoint to see if that resolves the connection.
2. If you have a firewall enabled, temporarily disable the firewall and open PowerPoint to see if that resolves the connection.
    - if this fixes the issue, you can go through the specific applications that are blocked by your firewall and allow PowerPoint and PresentationPro Express.