Lost my bitcoins, was I hacked?
If your bitcoins had been stolen (by someone else who acquired the private keys), your client would show transactions sending those coins to the thief's address.  The fact that you see no transactions at all suggests that for some reason the client has not imported the keys correctly, or perhaps that your backup is corrupt.  

If you know the addresses from your wallet, you can look them up on a site like http://blockchain.info and see if the coins are still in those addresses, or if they have been transferred out.