Since you got this from the internet I think the person you bought it from might be messing with you. On the iPod touch it is possible to limit how loud music is played, and a prankster might do this to you. To check if they did this:
- On your iPod, go to the Settings app.
- Scroll down to "Music."
- Choose "Volume Limit"
Here is where you would be able to find out if there is a volume limit on your iPod. If they didn't lock it then you can slide the volume slider all the way to the right, but if they did lock the volume, you have to go to option 2.
Option 2 is to restore it with iTunes. And this will fix just about anything that goes wrong with your iPod.
- Plug your iPod into iTunes and sync it.
- On the sidebar on the left, click on your iPod and go to the summary tab.
- Click on restore and let iTunes do its thing.
- After it is restored you should be able to put all of your music back on it and hopefully the iPod will be fixed.