Thanks everyone for your contributions on this simple issue.

Thanks too that I've learnt about Alt key.

I got the solution of this question anyway, I think I was't thinking when I asked in the first place. Thanks anyway.

Code:
'Check if there is duplicate UserName in the Database
MyQry = "SELECT * FROM UsersTable WHERE  UserName = '" & TxtUserName.Text & "'"
MyCmd = New OleDbCommand(MyQry, Conn)
MyCmd.ExecuteNonQuery()
DTR = MyCmd.ExecuteReader
Select Case DTR.Read
    Case True
        MsgBox(Prompt:="The provided UserName is not availble. Plese choose another one.", Buttons:=MsgBoxStyle.Exclamation, Title:="UserNameError")
    Case Else
        'If Username is available, save the information to the database
        Dim DBUserName As String = DTR("UserName")
        Dim _UserName As String = TxtUserName.Text
        MyQry = "INSERT INTO UsersTable(UserName,FullName,UserPassword) VALUES('" & TxtUserName.Text & "','" & TxtFullName.Text & "','" & TxtConfirmPassword.Text & "')"
        MyCmd = New OleDbCommand(MyQry, Conn)
        With MyCmd
            .ExecuteNonQuery()
        End With
        Close()
End Select