iTunes is not recognizing my iPod Touch 4th generation
First, try connecting to a different computer and/or using a different cable to rule out the possibility of it being something other than the iPod.

Next, check if there are any defects with the iPod. If you are using iOS 5, configure it to back up all your data to iCloud.

Finally, you may want to consider putting the iPod into recovery mode and trying to restore from there. If that does not work, you may want to visit the Genius Bar to check for any hardware issues. 

How to do it: http://support.apple.com/kb/HT1808

Note: if you are out of warranty, and suspect it may be a physical issue, you may just want to continue using the iPod as it is, because once you put it into recovery mode you may not be able to get out of it