How can we enable monitor power saving sleep?

Our PC has been upgraded from Windows 7 to Windows 8 Professional and did receive a new graphic card, Asus ATI HD 6450 fanless with three ports, DVI, HDMI, VGA. It replaces the Nvidia Geforce 7900 GS which became obsolete because it doesn't support HPCI (bluray player).

The monitor is a Samsung Syncmaster 245B 24" at 1920x1200 resolution supporting VESA-DPMS power saving. And is connected with the same DVI cable.

Using Windows 7, the monitor went to a monitor power saving modus as expected (Backlight off) and resumed immediately showing the last desktop image upon activating the keyboard or mouse.

Now at the same energy settings in Windows 8 Pro, the monitor would get black and showing the error message as a moving screensaver dialog box "No signal". Backlight is still on.

How to fix this? As far as I heard from the Samsung phone support, it's the graphic card which would send a dpms standby signal. Is this correct?

As it turned out, the DVI cable was not fasted enough to the port of the graphic card

Now DPMS is working. Topic is closed!