And what version of Windows do you use?
As a test, if you have not already, shut down (power off) your computer and disconnect all USB devices (including any hubs). You can leave standard keyboard/mouse connected, if used. Start up computer, run iTunes, and connect iPod (by itself) to a direct USB port on the computer. This checks for possible interference between connected USB devices "confusing" the OS, and that iPod is getting enough power from the port.
Also, do you happen to have access to a different computer that has iTunes installed? If you do, I would try connecting your iPod to that computer to see if there is any difference. This checks for a software problem on your computer.
If you have happen to have another USB docking cable, you should try it, to rule out a faulty cable as the cause of this problem.
And I did not ask earlier, but when you turn ON the iPod while it is disconnected, does it start up, show to its "Home" menu screen, and operate normally as an iPod?