Your mouse has disappeared from the screen and you no longer have control of your NVR.

Most of the higher end Uniview NVRs have a 'Main' and 'Aux' monitor.  The control has simply been moved from one to the other (whether you have a 2nd monitor connected or not).

To bring mouse control back to your monitor, simply right click the mouse for 7 seconds.  The mouse control will return to your screen.

That's it!  Good luck with the NVR!