Did you also tried reinstalling the spacedesk Driver on your primary machine?
And you still cannot connect anymore?
Does your viewer app disconnecting with error code/info? Or just showing "display off" status?
Did you check your display settings window (on primary machine) if you can find a detached secondary display?
Can you also click the spacedesk tray icon and check if the spacedesk SERVER window indicates a connected display (e.g. connection count is not zero) ?
For assistance, please also check the troubleshooting procedures in our user manual. https://spacedesk.net/user-manual/
For further analysis, could you please run dxdiag.exe on your primary machine, click "Save All Information" then save the output file (dxdiag.txt) and attach it on your next reply.
PS: Attach option should be visible after your second post.