I have a wireless network adapter which I would to use to wake up the computer, but it´s disabled (I can´t check it). I´m running windows 7 64 bits. Why is that?
We need more information about what wireless adapter you are using and the driver version.
Wake-on-lan (WOL) on wireless networks is a relatively new technology and not all wireless cards/chipsets support it yet.
You might want to check your BIOS to make sure that WOL is enabled, as many systems ship with WOL disabled by default and this might be why you can't enable it inside Windows.
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According to Realtek's documentation:
This means that you probably don't have the correct drivers installed and/or you haven't enabled Wake-on-Wlan in the BIOS. Make sure you download the correct driver straight from Realtek's page and then double-check your BIOS.
Remember that you're going to need a system capable of sending 'magic packets' to wake the system up. You also have to make sure that your laptop is capable of keeping the card powered up when it's asleep.
Personally, I don't believe in Wake-on-Wlan due to the nature of the wireless protocol and the amount of power that's necessary to keep the wireless card "awake" and listening for wake-up packets.