I thought you'd be the one to help, thanks! I have 2 machines on one monitor, and the online machine didn't have a problem, so I checked the cables, and figured it wasn't the monitor itself, but some hardware or software in the offline machine (win 7 GEForce GT610 with Forceware driver 378.66).
No, monitor didn't say anything, just turned black. On one or two occasions the machine rebooted by itself, at other times only the screen got black, but machine kept on running. Can't be overheating, it was just running a low intensity.
I'll work on, see if it happens again after having reinstalled the driver.