[SpeedyRO]

how i can make when exist a acount with the name "Exemplu" and somebody want to register with "ExEmplu" to kick him?

[RedJohn]

He can't register if already exist because it will force him to login.

[SpeedyRO]

he can..

[RedJohn]

Then your register/login system isn't good.

Follow some of those tutorials in 'Tutorials' section.