I don't understand why you would have to "buy <your> albums again" if you ripped them from CDs in the first place. What happened to the CDs?
Anyway, it's unlikely that iTunes is deleting your music, why should it? Presumably though, the album tracks are still referenced in your iTunes Library but with an exclamation mark to the left of the title, indicating that iTunes cannot find it. This would happen if iTunes can no longer locate the song file, and that would happen if the file was moved, renamed or deleted.
- Have you moved the file after importing it to iTunes?
- Did you rename the files in Windows Explorer after adding it to iTunes?
- Are your songs located in the iTunes default folder, or are they on an external drive? If they are on an external drive, that drive needs to on and ready before you start iTunes.
- Is it possible that another programme you have on your machine is moving, renaming or deleteing the files?
- Have you looked in the folder where the songs were originally located? Is the folder still there?