I lost all 300 songs from the iPod

Where did you get the songs in the first place? Go back to there and get them again.

• If the iPod you found was an old one of yours, isn't the music still in your iTunes Library? In which case, just Sync the iPod with that iTunes Library to put them back onto the iPod.
• If you simply "found an iPod" - that is, it wasn't your iPod, but someone else's, then the music on it is not yours to own or to have (even if you had paid for the iPod).
• If the iPod and the music was (and still is) yours, then;
  • If you imported from CDs, re-import from them again.
  • If you purchased from a digital store (such as iTunes or Amazon), go to your account and hopefully, you should be able to download them again.

Syncing is one way, from iTunes on the computer to an iPod, so I'm going to make a guess that you have synchronised the iPod with an iTunes Library that did not have the music (on the iPod) in the Library, which is why it has all beeen deleted from the iPod. Regardless of whether Apple told you to do this, you would have seen a warning telling you that Syncing the iPod with your Library would erase all the content on the iPod. Did you simply ignore the warning?