sounds to me like you're going into S1 state on the other computer, and S3 state on the Windows 7 machine. S5 would be "fully cut off".
The culprit could be in your BIOS, make sure wake-on-lan or WOL from S3 is at least set to on (also could be under PME). the second thing is to check actually in your network card's driver
, which probably also has a setting, by going into Control Panel->Device Manager->Network Adapters-> right click on yours, then go to Properties. You should have a "Power" tab under that, which you can also set these settings. Make sure "Allow this device to bring the computer out of sleep" or "Wake from Magic Packet" is checked/enabled. This may also be under the "Advanced" tab or something similar.. just poke around.
Ultimately, though, you need to have it enabled in both your BIOS and your OS/driver. There is also a neat/tiny program I have that will do it and allow you to listen on your network for magic packets/wake requests... that I know works to bring my Windows 7 machine out of S3 mode. As soon as I can find a link for the site I'll post it [edit: WOL for Windows, use WOL Monitor/Sniffer to test if it's working]. Here is the link: http://www.depicus.com/wake-on-lan/wake-on-lan-gui.aspx
I can confirm this program works to bring Windows 7 machines out of S3 mode, if properly configured.
Also, where are you trying to wake the computer from? Inside your local network (LAN) or from the Internet? Another consideration could be the port is being blocked.
Here is a great article for you: http://smallnetbuilder.com/lanwan/la...n--wake-on-wan
and another one from intel, http://www.intel.com/support/network/sb/cs-008459.htm