I m trying to open GUI-wallet and have error "Bytecoin wallet already running".
What should i do?
Are you running any other cryptonote coin wallet at the same time?
No, only sikka gui-wallet.
Close your wallet and then open your resource monitor. See if you see wallet.exe running .. if so end the process. Then open your sikka wallet again. See if that helps.

1) I m trying, as you say, but it not helps - only "sikka.exe" running in the resource monitor.
2) Trying run sikka wallet as administrator and it change the error - Loading screen of GUI appears
(with logo) and stuck - say "Blockchain load error".