why can't i sync my itune library to my ipod anymore

You may need to set up or update the iPod's settings for automatic syncing.

First, if the iTunes sidebar (along left side of iTunes window) is not visible, from the menu bar, under View, select Show Sidebar.

Find the iPod in the sidebar, under DEVICES, and select it. There is a bar of buttons toward the top, starting with Summary. Click on Music next to Summary. This is the iPod's Music screen, where you tell iTunes how to sync songs to the iPod.

The checkbox for Sync Music should already be checked, if you have been using automatic syncing. If that checkbox is NOT checked, your iPod is currently set for manually loading. If you check Sync Music now (and Apply the change), any songs that are on the iPod that are not in your computer's iTunes library will be lost. So, if there are songs on the iPod that are not in your iTunes library, do not proceed...

Otherwise, check Sync Music, if it's not already checked.

You can choose to sync Entire music library, if it will fit on the iPod. With this setting, your entire iTunes music library syncs to the iPod. Any changes to your iTunes music library sync automatically to the iPod, the next time it is connected (or when you click Sync).

Otherwise, you can choose to sync Selected playlists, artists, albums, and genres. Then, select (checkmark) the playlists, artists, albums, and/or genres you want on the iPod from the lists below. If you want new songs to sync to the iPod, they must be part of your selection. For example, you can add them to one of the playlists that you have selected for syncing to the iPod.

When you click Apply, the songs from your selection sync to the iPod. Going forward, changes to your iTunes library (based on your settings on the iPod's Music screen) sync automatically to the iPod, the next time it is connected (or when you click Sync).