Currently Being ModeratedApr 7, 2012 8:08 AM (in response to Jelliapple)
The exclamation marks happen when the files are no longer where iTunes expects to find them. Possible causes are that you or some third party tool has moved, renamed or deleted the file, or that the drive it lives on has had a change of drive letter. It is also possible that iTunes has changed from expecting the files to be in the pre-iTunes 9 layout to post-iTunes 9 layout,or vice-versa, and so is looking in slightly the wrong place.
As you say, FrostWire would seem to be the culpit here. You probably want to uninstall it, but it might be best to try to repair your library first.
Select a track with an exclamation mark, use Ctrl-I to get info, then cancel when asked to try to locate the track. Look on the summary tab for the location that iTunes thinks the file should be. Now take a look around your hard drive(s). Hopefully you can locate the track in question. If a section of your library has simply been moved, or a drive letter has changed, it should be possible to reverse the actions.
Alternatively, as long as you can find a location holding the missing files, then you should be able to use my FindTracks script to reconnect them to iTunes .