Lenovo ThinkCentre Edge 71 not showing anything on screen

Hi,

Have you proved that the monitor is OK i.e. has it got a menu screen e.g. brightness, colour contrast etc that you can access by pressing the controls on the monitor to prove that the monitor is working OK?

Is the HDD activity light on, next to the power LED on the front of the case?

Does the computer "beep" when you first start it and if so how many beeps?

does it happens recently?

had you connected to the correct place? AFAIK some might have add on graphic card which you need to be connected there if it has been installed, not on the mainboard directly .