Anyone know why my Ipod Touch won't wi-fi sync with my win 7 PC unless it is usb connected to it?

Question

According to latest Apple IOS release 5.1.1 I can wi-fi sync my IPod to ANY networked PC hosting its ITunes as long as the IPod is connected to a power source and its wi-fi is enabled.  Well...doesn't work ("Sync Now" button is not enabled). It IS however enabled if I connect IPod to the windows 7 pc via usb cable. Of course, this option is then superflous as I am capable of syncing the device via the faster USB connection instead.  Isn't it supposed to work if the ipod is connected to a power outlet, or my Macbook Pro and the Windows 7 PC and Itunes are running and on network?  What's the point of the feature otherwise?
Reason I would ilke to do this is that my music library is housed on Windows 7 PC (it has more storage space then my MacBook Pro), but I often recharge it connected to my MacBook Pro  This is a nice to have, but hardly necessary feature, but  if someone has a solution I would love to know about it.
Possible error on my part:
I enabled this feature while IPod was not connected to any device.  (later read that one should enable the feature while iPod connected to PC).  The "sync now" button is not enabled UNLESS I connect the ipod to the Windows 7 pc by usb cable.  THEN the "sync now" is enabled.  What do i do to correct?   

Answer 1

I synced iPod touch to a desktop wirelessly connected to a router. 
Searched the forum and found 3 useful suggestions.
1.  check the firewall log to ensure there was an exception allowing applemobiledevice.exe to clear the firewall, if it is blocked.
2.  Verified the desktop was accessible via wi-fi.
3.  Connected iPod to the desktop using the usb cable,
ran iTunes,
clicked the iPod device icon to open the Sync window,
clicked the SUMMARY tab and
scrolled down to the checkboxes.  Checked the box for "wi-fi sync". 
Then SYNCED the iPod via the cable. 
Then disconnected the iPod from the cable without clicking the EJECT icon.  This leaves an established sync connection on iTunes.
Quit iTunes, then reloaded it to ensure the iPod device icon still appears under DEVICEs in iTunes. 
I wonder if you are having problems with the wireless transmitter?  I've had them burn out in the past.  Replaced a router that died, and had a dell laptop whose wi-fi xmit/receiver died.
Also had to re create the wireless network setup on the desktop.  Not sure why but twice have had to recreate it when it quit working.
I sympathize.  it's a pain in the butt dealng with networks.