<li class="dropdown">
                        <a class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false"><?php echo $_SESSION['nome']; ?><span class="caret"></span></a>
                    <ul class="dropdown-menu">
                        <li><a href="MinhacontaPt-BR.php">&#128102; Perfil</a></li>
                        <li><a href="../Conexao/sair.php" class="fa fa-sign-out"> Sair</a></li>
                    </ul>

<li class="dropdown">
                    <a class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">&#128102; Minha conta<span class="caret"></span></a>
                    <ul class="dropdown-menu">
                    <li><a href="CadastrarPT-BR.php">Registrar-se</a></li>
                    <li><a href="loginPT-BR.php">Entrar</a></li>
                    </ul>
                    </li>

<?php
echo 'Hello world!';
session_start();

<?php
session_start();
echo 'Hello world';

<?php if (isset($_SESSION['nome'])) { ?>

    <li class="dropdown">
      <a class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">
        <?php echo $_SESSION['nome']; ?><span class="caret"></span></a>
      <ul class="dropdown-menu">
        <li><a href="MinhacontaPt-BR.php">&#128102; Perfil</a></li>
        <li><a href="../Conexao/sair.php" class="fa fa-sign-out"> Sair</a></li>
      </ul>

<?php } else { ?>

    <li class="dropdown">
      <a class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">&#128102; Minha conta<span class="caret"></span></a>
      <ul class="dropdown-menu">
        <li><a href="CadastrarPT-BR.php">Registrar-se</a></li>
        <li><a href="loginPT-BR.php">Entrar</a></li>
      </ul>
    </li>

<?php } ?>