They are not BTC, they're testnet-coins.
Exactly. There is nothing to recover here.
You can just play around with this high amount test net btc, but they are worthless.
Just a quick guess, has somebody sold you a bunch of "BTC" for cheap, but somehow convinced you to use a client in testnet-mode sometime in the past?
If so, you might have been the victim of a SCAM.
Most probably a scam.
Please give us more information so the user who sold this coins to you will be properly tagged and we can open an scam accusation against him (or his website) so he doesn't scam anyone else so easily (at least here in this forum)