Could you expand on “was working fine” before? Had you been using it for long? And recently? Or was this the first time you restarted?
Maybe start troubleshooting by …
Spaces can be an issue for navigating / typing file names when on the command line, and so what is happening in ‘Snap 2’ isn’t that shocking. In your Windows file browser (‘Snap 3’) can you copy one of the files and rename it to a short name with no spaces, such as testcp.ipynb? Then back in your system command line interface (like in ‘Snap 2’) type, jupyter notebook testcp.ipynb. Did that open the notebook? (I’m assuming that has worked to open notebooks before?)
Do you see the new notebook when you type dir back in system command line interface (like in ‘Snap 2’) ?
(Suggestions here may help you in what else try.)
Another direction to try for troubleshooting…
From the Jupyter Dashboard that you show in ‘Snap 1’, open a new terminal using the New button on the right side. And in that type terminal type pwd. That should tell you where things are starting with the default working directory. You’ll want to see using ls and cd how to get from there to your directory with notebooks and that may inform you on how to do that in the dashboard.
Once you get the notebooks working again, you’ll be dealing with Windows-specific path issues calling file names from inside the notebooks. See here if you aren’t familiar with this. (The comment by furas here can help in understanding why this is so.)