Ipod Touch Problem!!!?

So I plugged in my iPod to my laptop the other day and saw that my iPod needed an update. So I decided to do it. Since I updated my iPod, all of the I bought on within the past () year will no longer play. I try to click on a song, and it just skips right to the next one.
It’s only music that I have bought the iTunes store my iPod. Not all of it, it seems to be only the more recent stuff.
This is frustrating me so much because its over $30 worth of music. If anyone can help me out, it would be greatly appreciated. I have no idea what to do.

A Question About Backing Up Ipod Content?

So I want to update my iPod 4th Generation, but it said that if I did it would delete all and media(which I presume is ),I have backed up the iPod to the computer I am using to update it… Does that mean that if absolutely anything happens, and I update it and delete things and install things as I please, I will be able to restore my iPod to what it is right now, and nothing will be different?
Thank you for answering!