Reset start and stop times for songs in iTunes

For some reason some of songs in my iTunes library have the start and stop time set so the entire song is not played. I tried selecting my entire library and then "Get Info", but the "Multiple Item Information" box does not allow me to change the start/stop lengths for more than one song at a time.

So how can I change these settings for my entire library (I want to remove them so I get the whole song) without having to select each song. With over 2000 songs in my library and no way of knowing which ones are 'infected' without testing each one, it simply is not practical to do it manually