I have bought Premiere Elements 2020 with online licence. It works - but always just for the first time. When I close the programme and want to reopen it later, it does not work. I have to restart computer. I have already tried the advice from thread "Premiere Elements 2019 / Cannot launch video editor" - launching it from C:\Program Files\Adobe\Adobe Premiere Elements 2020.
I've had this happen a couple of times too. The problem is that the program doesn't close completely.
Assuming you're on Windows, open the Task Manager (by right-clicking on the Windows Task Bar and selecting the option) then go to Background Processes, locate Adobe Premiere Elements and manually end it.
As already stated by Steve, this might be because the application was not closed properly. If you are facing this issue frequently, you can create a dump file for the process running in backgroud and share with us so that we can permanently fix the problem.
To create a dump file:
1. Open Task Manager.
2. Select the process "Adobe Premiere Elements".
3. Right click on the process and select "Create dump file".
4. Share the dump file on Google Drive or drop box.