where are my songs?

Hi, folks!

I have an iPod classic that had over 4500 songs on it. Last week due to a glitch in the system, new music I bought wouldn't sync automatically so I was able to sync it manually. I then re checked the box for automatic sync. I see in my itunes library that there is the cloud near each song. When I downloaded my new songs, none of my old songs came up. I reinstalled them by clicking on the cloud and it downloaded into my iPod. My problem is that thousands of songs did not, and I cannot find them at all in my library. The songs were not grouped into albums, for instance. It seems that the only songs I was able to keep were those I bought from itunes. Where can my other songs be, could they have been removed? How can I remedy this? Has this happened to anyone else?

THANKS!!