Missing I-tunes song data

So I bought a new laptop (windows 8) and transferred my music library (about 7,000 songs) from my old laptop (windows 7) to my new one. After installing i-tunes, I was surprised to see that about a half of my songs have some aspect of their song-data missing (album, artist, tack title, year, artwork, genre). A few hundred songs have all their data missing except for their track name. I looked at the file properties on windows and all the data is inserted correctly, also windows media payer displays everything fine, but i-tunes messes everything up. I've tried several things but nothing works (re-installing i-tunes, updating to the newer version, adjusting all library settings in the preferences). I've deleted my library and tried to re-transfer my songs, but the same thing happens to the same songs. When I enter the data into the "get-info" it does remain, but I really don't want to manually enter all the data over again. Any ideas of what to try next?