Itunes Library Lost After Upgrade 9.0

First let me say that I am so new to mac until I feel like I am in a foreign country. I purchase this mac from the pawn shop, because it was it a good deal, and heck let's face it; it probably was the only way i would have ever gotten one...Anyway - My new mac came with approx 2500 songs already on it(Awesome!!). Well, while trying to be a Santa Helper on Xmas Eve, I purchased new music (Itunes) & loaded them on my daughters new ipod. When I plugged in her ipod; Mac said I needed to upgrade to a newer itunes version- DONE! - new music loaded to her ipod (no problem). I shut the Mr. Mac down; woke up a few hours later; I wanted to play music - ALL MUSIC WAS GONE (AGGHH!)(Nervous Breakdown was about to occur!). It said that because a newer version was installed it couldnt read my library (oh goodness - my life is over); I went online - to get pointers & nothing seem to be directed towards itunes 9.0 upgrades

PLEASE HELP - I dont have every much enjoyment in life & all I wanted for Xmas was to listen to the music that I purchased 4 me for Xmas from itunes (sniff-sniff)..

All of your music is gone? Have you checked your iTunes Music folder?