getting rid of ! marker on songs in my itunes library

[Chad Leigh]

I have most of my iTunes stuff stored on a network disk.  When I last  
udpated iTunes a day or two ago with the latest version, it "updates  
the library" and since the network disk was not yet mounted, it  
marked every song with a "!" indicating the song was "missing."

I mounted the disk and it can play any song I click on.  But the !  
are there for all the songs I have not yet played, which destroys  
shuffle play or just playing a playlist automatically as that only  
plays the ones it thinks it knows are there.

This happened to me once before and I cannot remember how I told it  
to re-find the songs en masse in order to get rid of the !.

Can someone help me out.  None of the menu items seem to do it.

Thanks
Chad