Monitor does not sleep with Intel HD4600

Hello.

I recently bought a laptop and I use it with a Benq 24inch monitor via HDMI. The problem I have is the monitor does not sleep when Windows commands it ( it goes black and the backlight is on). I tried all the settings in power options and in BIOS I did not find any settings regarding video or power settings. The problem is not from the cable/monitor for sure because it works well with a Toshiba laptop that uses an Ati hd4650 video card.

The laptop informations are:

Intel i3-4000m

Intel hd4600+ati 8750m

Windows 7 64bit

Thanks !