what the hell?

??
I downloaded new block chain, and all my mined coins are gone?

If you're mining without a blockchain downloaded, you'll get truckloads of blocks... none of which are attached to a blockchain other than your own personal meaningless blockchain.
When you replace your meaningless blockchain with the blockchain that everyone uses... POOF~! There goes all your previous meaningless mining.
I've done that before by accident. (I forget which coin I was mining... blockchain wouldn't update and I had TONNES of blocks - got really excited for nothing.)
Now, I don't know if this is exactly the same situation as what you had there, but I've done it before, and it might help explain what happened for you.