I have done this before but now when I hit my iPod only pictures show up. My music shows up on the device in iTunes, but not on the computer. I have tried to show hidden files but nothing appears. Please help, I really need my music on my computer!
The iPod touch much like the iPhone do not reveal the internal Library to the Windows explorer (or OS X Finder for that matter). They only allow access to the picture folder. This has been locked down within the iTunes USB driver.
You will have to use one of the many tools available to copy the music to your computer. I suggest you look at the following Q&A and try one of the tools suggested there.
Something like CopyTrans (http://www.copytrans.net/) will do the job nicely, it's not free but depending on the value you assign to the music it might be a worthwhile purchase.
As far as I'm aware it copies from iOS/iPods to your PC, then you'll have to re-import the music back into iTunes. Check first though, as I haven't personally needed to use it myself (though I've heard some good things).
Have you read through the trouble shooting on the Apple support site?