Try the following:
If you create a new user on your computer, does iTunes stop responding when you connect the iPod or iPhone when logged in to a new user? Please make sure you logout of the original user instead of switching users.
If it is fine in the new user, try creating a new library in the original user account on your computer.
How to open an alternate iTunes Library file or create a new one
This explains how to use iTunes 7.0 or later to choose a new or different iTunes Library. This can be use to verify or isolate issues, or just if you want to easily choose different libraries.
Steps to create or choose a different iTunes Library file
1. If iTunes is running, quit iTunes.
2. If you are using Windows, hold down the Shift key and from the Start menu and choose All
Programs > iTunes > iTunes.
3. If you are using the Mac, open iTunes and immediately hold down the Option key.
4. You should see & follow the 2 screens "choose library"
Additional information
If you do not see one of the screens, then you did not hold the correct key at the correct time. You may want to try again. Note that if you pinned iTunes to the Start menu programs, and open it that way, it may not work.
Rebuilt. Switch back to your original library following the steps in the above link, and then try this:
Re-create your iTunes library and playlists
Re-creating the iTunes Library file
1. Quit iTunes.
2. Locate your iTunes folder.
3. Open your iTunes folder.
4. Drag the iTunes Music Library.xml to the Desktop
5. Drag the following file from your iTunes folder to the Trash:
6. Open iTunes.
Important: Do not add any content into iTunes at this point.
7. Choose File > Library > Import Playlist.
8. Navigate to the iTunes Music Library.xml file on the Desktop.
Mac users: Click Choose.
Windows users: Click Open.
After re-creating your library, any devices that you sync with iTunes (Apple TV, iPod, iPhone) will see your iTunes library as a new library and will completely resync.