que no le falta los ID a loggin???
<form name="form2" method="post" action="entrar.php" id="form2">
<p><span>Nick Name: <input name="username" type="text" id="username" /></span></p>
<p><span>Password: <input name="password" type="password" id="password" /></span></p>
<p><span><input type="submit" name="Submit" value="Entrar a Partida" /></span></p>
</form>