Does it show "Display OFF" status on your viewer app?
Did you check the display settings on your primary machine if there's detached secondary display/s?
For assistance, please also check troubleshooting chapter on our user manual https://spacedesk.net/user-manual/.
For further analysis, could you please send us the following:
- run dxdiag.exe on your primary machine, click "Save all information" and send us the output file (dxdiag.txt)
- spacedeskSetup.log file located in C:\Users\Public
Please save all requested files in one folder, then right-click -> Send to -> Compressed (zipped) folder, then attach the *.zip file on your next reply.
PS: Attach option should be visible on your side after your second post.