tracks disappearin

Why does my library of ripped tracks disappear from my IPod when ever I purchase downloads from I Tunes? Took ages to rip 2500 tracks from my CD collection and now only left with purchased tracks. Now when I pop in a CD to burn, it will only copy to my library and not anywhere else on my PC.

Is it worth paying for I Tunes cloud, so I can create a permanate file of my CD collection? Any other suggestions to have my CD collection available in a folder to upload to my IPod, instead of ripping to library, then losing them and having to start again