There's many reason why those two doesn't seem to work. But thanks to Kioskea.net, I was able to find you the answers.
1. Your computer or iTunes is not to blame. Blame your iPod.
Hold your menu button down for about 15 seconds, let it reboot, and plug it back it in to your computer again, your computer should then recongnize your iPod.
If the first option doesn't work, here's my second option:
2. Plug in your iPod, and put it into Disk Mode. Hold the menu button, and let it reboot (Don't forget to leave it plugged in)
Now in your computer, go to your Control Panel. In your Control Panel, open System and click the Hardware tab. Once there click Device Manager. Find Universal Serial Bus Control, right- click Apple Mobile Device USB Driver and uninstall it. (If if's not installed with iTunes, get it)
If all these doesn't work, I guess you could just pray and unplug and plug your iPod.
Hope this helps!!!