So I upgraded my onboard HD 4250 to a GeForce GTX 660 and ever since my monitor is not going into proper Standby mode (=black screen, orange led color, not green), instead when the computer is idle for the predefined set of time (power options) it shows the "No Signal" banner boucing on the screen forever.
The only difference beyond the obvious (different graphics adapter and drivers) is the connection:
I used to connect the monitor through D-SUB to the onboard 4250, but now I'm using a D-SUB - DVI converter since the 660 only has DVI's and my big old CRT has only D-SUB.
I haven't used any drivers for my monitor because there is none for 64-bit, so it used and still using the default generic non-PnP drivers.
There's no problem waking up the monitor.