i had the same problem so i read through this thread. i tried most all of these and they did nothing on their own until i ...
1) unplugged my itouch from the pc's usb port and plugged it directly to the walls a/c power and
2) restarted my pc
i then restarted my pc and reconnect via the usb port.
so i would try 1 & 2 first since it's the quickest route and it was then i actually saw any type of result.
however prior to that ....
did a restore of my itouch software - which took a while to download
turned wifi sync on/off
did the reset warnings option
checked for updates to my itouch
downloaded the latest version of itunes
all to no avail until i finally did 1 & 2
not sure what the combination was but i'm up and running again