Please help

As a test, to rule out a problem with the USB port, shut down (power off) your computer and disconnect all USB devices, including hub, except for standard keyboard and mouse (if normally used). If your computer is a laptop, connect its power adapter (so that it's not running on battery power). Do this to reset your shuffle

http://support.apple.com/kb/HT1655

(There is no "5G" shuffle; your shuffle is 4th gen.)

Start up computer, run iTunes, and connect shuffle to a direct USB port on the computer. If it still does not work, try connecting something else to that USB port, preferably something similar like USB flash drive, to confirm it is working.

If that does not help, you should also rule out faulty USB cable as the cause. To do so, you'll need to try a different USB cable with your shuffle, or try the one you have with a different shuffle. If that's not possible, and you have an Apple Store nearby, you may want to make a reservation at the store's Genius Bar. Take your USB cable along, to confirm it is working (or not working) properly.

If you can rule out the USB cable, it is likely that the problem is the shuffle itself. If it's four months old, it is covered by the one-year warranty against defects. You can take it to the Genius Bar at the Apple Store, or contact Apple Support (use Contact Us link at bottom left corner of this window).

If the shuffle is under warranty (at four month it would be under warranty), and the problem is a defect (not accidental damage), it will likely be replaced, not fixed. If it is not covered under warranty, the cost to repair is likely to be more than the $49 for a new one.

In any case, since you have another shuffle and it works with the same USB connection and cable, I think you have already ruled out everything except for the shuffle itself. You should contact Apple, either at an Apple Store Genius Bar, or through the "official" contact link.