You updated Itunes on your computer but now all of your songs tvshows etc are unplayable and they all have an exclamation mark in a circle before them how can you fix this?

The exclamation mark indicates that iTunes has forgotten where the library of music/videos is located. If there are not too many you can double click on the individual titles and then show iTunes where the file is located - on a Mac that is usually in the iTunes folder within the Music folder (on a Windows machine it will be something like My Documents/My Music/iTunes/iTunes Music/). With iTunes 10 it is smart enough to know that most of the other missing files will be in the same place and so it will ask you if you want it to check for the other missing files at the same location.

Alternatively you can try opening iTunes preferences and under the Advanced tab click the Change... button to show iTunes where the media library is located. Or drag the required files from the Music folder back into the iTunes window so it rebuilds the library.