Premiere Pro was working on my Mac. Then I erased the HD and reinstalled my OS. Now it won't work?

Which version of macOS is that MacBook Pro running? The 2024 versions of Premiere Pro now require macOS 12 (Monterey) or newer in order to even install at all. Your MacBook may be currently running MacOS 10.15 (Catalina), which is what your MacBook originally shipped with, or macOS 11 (Big Sur), which is why Premiere Pro would not install at all. If you're still running Catalina, then none of the currently supported versions of Premiere Pro will even install at all! This signifies that you might have never updated macOS at all.

Therefore, you MUST update your system's macOS before you can even install Premiere Pro at all. The current version of macOS stands at version 14.3.1 (the latest build of Sonoma).

I see this on the System Requirements: 

Note:  it is not possible to install the 24.x versions on Intel® 3rd Generation of processors or older (as well as older AMD processors).

Here's the requirements page: https://helpx.adobe.com/premiere-pro/system-requirements.html

@RjL190365 might know the specifics. Is it your graphics card?