I tunes music disappeared

I have well over 9,000 songs downloaded mostly from cd's onto my MAC, while all songs are listed, some are highlighted with a blue cloud and downward pointing arrow, while others are not highlighted and no cloud. The highlighted songs will play while the others will not. Also, I lost one complete playlist. I also cannot sync my iPod now. Of course I do not want it to sync while it is in this configuration. Can you help me?