I would first try out the following steps:
- Quit iTunes.
- Download and install the latest version of iTunes.
- Use the Finder (Mac) or Windows Explorer (Windows) to go to the iTunes folder that contains the iTunes library files:
Mac OS X
Microsoft Windows Windows XP and Windows 2000
\Documents and Settings\username\My Documents\My Music\iTunes\
Microsoft Windows Windows Vista and Windows 7
- Drag the iTunes Library file from the above location to the Desktop.
- Open the Previous iTunes Libraries folder in the iTunes folder.
- Locate the file named iTunes Library YYYY-MM-DD where YYYY-MM-DD is the date you upgraded iTunes (Year-Month-Day).
- Drag this file to the iTunes folder (the enclosing folder).
- Rename this file to iTunes Library.
- Open iTunes.
You should now see your missing content in iTunes.
If that doesn't work, I would try removing all traces of iTunes then reinstalling by following the directions in this document:
Have a great day,