I am having the same type of problem, if I reboot my PC, I can preview song until I switch over and start a song, then going back to preview I get nothing. Just the song name like it is trying to download but no sound. Then when switching back I get no sound out the library, until I close ITunes and reopen it then I get sound from my libary. I then have to reboot my PC to should from another preview.
This is what apple told me to do For best results, your network connection should be able to download at 128 kilobits per second (kbit/s) or faster, particularly when listening to previews of songs. A DSL, cable modem, or local area network (LAN) Internet connection is recommended.
On slower network connections, you may wish to enable the option to load the complete 30 second track preview before playback begins. To enable this option, open iTunes, and choose Preferences from the iTunes menu (Mac) or Edit menu (Windows). Click the Store icon, ensure there is a check by "Load complete preview before playing," and then click OK.
If this does not help, I recommend that you attempt to resolve this issue by uninstalling iTunes and QuickTime, and then reinstalling the latest version of each. To do this, first ensure that you are logged in to an Administrator user account on your computer, then follow the instructions in these articles:
After trying that, I sent another email asking for help and I received this information. "The question you asked falls outside of my area of specialty, but Apple does offer some resources that should help you" try the boards, upon surfing I see a few post with the same problem.
If you require more in-depth assistance, you may wish to call our AppleCare technical support team. A representative will be able to tell you about Apple's complimentary and fee-based support options and can help you determine which option might be most helpful in this case. To find the appropriate phone number, please visit:
http://www.apple.com/support/contact/phone_contacts.html
Does anyone know where to start is it sound card related?