in the bicoin.conf file i can see these :
rpcuser=generated_by_armory
rpcpassword=43 long string
so this means nothing ?
Yes, this means nothing. That password allows Armory to communicate with bitcoind, but has no relation whatsoever with the Bitcoin-Qt wallet password.
is it possible that i have never created any wallet in armory but after i installed armory some way i attached my bitcoin qt wallet to armory and it showed up in armory as a wallet and i set a password/passphase for it (that probably created those entries in bicoin.conf file) and so now i cannot use old passphase in the bitcoin qt wallet beacuse armory take control over bitcoin qt ( not allowing transactions from bitcoin qt)
No, that is utterly impossible. Armory does not import anything automatically (and in fact importing the Bitcoin-Qt wallet is both cumbersome and discouraged, it is not something you do by accident. And it is not possible with newer versions of Bitcoin-Qt). Even if you manually imported the Bitcoin-Qt wallet into Armory, that would not prevent you from still using the wallet in Bitcoin-Qt. Armory NEVER touches that wallet. Never.
(if i create a wallet in armory and i can see my whole btc balance in armory in this wallet , can i see my whole balance in bitcoin qt too or will it be empty ? )
That depends. If you
imported the private keys from Bitcoin-Qt (which is by the way only possible if they were created with an old version of Bitcoin-Qt), then you would see the coins in both wallets. If you moved the coins, then they would only be in Armory. But you would still be able to unlock your Bitcoin-Qt wallet with your Bitcoin-Qt password, and see the transactions, including a large one sending all the funds to Armory.
If your passphase does not work, then your Bitcoin-Qt wallet is either corrupt, has been removed (check backups) or you used another passphase than the one you think you used. Nothing Armory can do can cause this problem.