I had the same error and I was able to fix it. Just follow this steps. It will help you to solve the Error: cannot find module ‘discord_desktop_core’ message on Discord boot: 

• Uninstall Discord, move to your Control Panel and select: Select Programs > Programs and Features > Uninstall discord
• Delete the following folder on your machine: AppData\Local\Discord
• Delete the following folder on your computer: AppData\Roaming\Discord
• Download the latest discord from the official website and install discord again.

I had the error multiple times now. I cannot say why this error comes up but those steps allways fixed the issue for me.