You've done a couple of things wrong in posting here:

1) This is the Bitcoin area - you should move this to the altcoin section (see move bottom left of screen)
2) The board rules stipulate that you shouldn't bump your thread more than once every 24 hours.

That being said, try this:

Shut down the Litecoin QT Wallet.
Paste your backed-up wallet.dat into your Litecoin data directory.
Restart Litecoin QT wallet