So this sucks of course. Here's a few things you can check before throwing out your computer machine through the window (we actually don't recommend you ever doing that) 🤣
Which version of Sketch do you have? We support from v68–73+
Which version of OSX do you have? We support Catalina + Big Sur
Have you activated your Sketch2React license?
If you use any cloud services (Dropbox, iCloud, OneDrive etc) make sure you actually have the Sketch files downloaded locally on your computer machine
For troubleshooting make sure you use one of our newer free demo files, it can be that something is broken in older versions of them
Use our Sketch assistant to debug your Sketch files