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 it 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".
Are you running the cli-wallet along with the gui wallet? And with what parameters you start the sikka.exe with?
Also try renaming the sikka data directory (c:\users\\AppData\roaming\sikka) to something else, so that the gui wallet will sync it from the scratch.