What is the Mac OSX?
If you have not already, please see System Requirements
1. Latest version of QuickTime installed on computer?
2. Problem exist with and without antivirus and firewalls disabled?
3. Video card/graphics card driver up to date according to web site of manufacturer of the card?
4. You say that Photoshop Elements works fine...is that Photoshop Elements 14 and was that part of the Premiere Elements 14 Mac purchase?
Let us start here and then decide what next based on the details in your reply.
The OS X is Mac 10.11, El Capitan.
It worked when I enabled the firewall! Thank you.
Thanks for the follow up with the great news "It worked...."
Did you mean that you disabled the firewall or set permissions to prevent it from blocking any downloading installing of any important Premiere Elements files?
You did a great job sorting through the troubleshooting to gain your success.