Signal to monitor is lost during PC scan

I am new to Comodo Antivirus and am trying to run a full system scan for the first time. The scan runs for around 45 minutes then the signal to the monitor is lost forcing a manual shutdown (and failed scan). As far as i can see there are no conflicting programs (just uninstalled Windows Defender in case this conflicted), but the problem wont go away. Any ideas anyone? (i run two PCs from one monitor could this be an issue?).
I’m not too computer literate so any solutions in (very) simple terms would be welcome Thanks Django1

You use a switch to connect the two PC’s to the monitor? It shouldn’t cause an issue.
Any chance the Monitor is going to sleep mode due to lack of activity from you?
Does moving the mouse when this happens bring the screen back (albeit with a delay)?

sounds like the monitor is shutting down, go to control panel, power settings. You can change the option on when the display is turned off. You should be able to bring it back by moving the mouse or hitting space bar on the key board.