there was a software for wake on lan applications, magic packet if i recall, it was able to power on or power off many computers ... You have to configure thru the bios, the wake on lan option if it exists ??? , and in windows / power options / advanced option, there was an option to permit the computer to wake on lan events, something like that in windows 7 ???
I use iTalc, is a litle bit confuse to configure but is the way I wake, block, unblock, and shutdown remotly clients (students PCs). Take a look http : // italc.sourceforge.net. it's opensource software.