Welcome to the community. 
First of all, Launch Task Manager locate all WeMod processes (ie, look in background processes too). Then right-click and end task on all WeMod processes. And then re-launch it.
Other than that, antivirus interference can cause the software to not launch or install correctly, even if it’s just Windows Defender - it’s still an antivirus. Follow the steps in this post here: Can’t Install WeMod.
Keep us updated.