I have setup a schedule for disk defragmenter but in Task Scheduler i cannot see the option for a laptop waking up and not switching screen. Since my laptop has always its lid closed, i don't want the screen to turn on.
Windows 7 Enterprise 64-bit
There is a difference between the screen turning on and the backlight turning on.
Generally, when the lid of a laptop is closed, the backlight is shutoff to preserve power. And whenever the laptop is on, whether the lid is open or closed, the screen is always on.
This is because the display LCD is relatively low power compared to the backlight.
In a dark room you should be able to see a very dim image on the laptop screen where the backlight is off (or failed), but in a bright room the image will generally be so dim as to be very difficult to see, and even in a dark room, you could not use a screen without the backlight on.
If your laptop backlight is coming on when the laptop is woken up, I recommend updating your system BIOS (that usually has lots to do with power management). Also, check your screen brightness settings for the various power settings, as these deal directly with the backlight.