It's quite possible that it's your ethernet adaptor causing the problem.

If you go to Start menu type in devmgmt.msc into the search box, then press continue, when the window loads look for Network Adapters, then look for Ethernet, right click on ethernet, go to properties, then power management, look for a tickbox with text alongside saying allow this device to wake the computer. If it is ticked, untick it.

Also check your wireless card to see what power settings that is on also.