I Need help in php login form =/

<?php
					if(!$_SESSION[username]){
					?>
					<form>
                	<input name="username" id="StrUserID" class="logincamp" placeholder="Username" onblur="this.style.opacity='1'" onfocus="this.style.opacity='0.75'" type="text">
                    <input name="password" id="password" class="logincamp" placeholder="Password" onblur="this.style.opacity='1'" onfocus="this.style.opacity='0.75'" type="password">
                    <input name="login" value="" id="login1_btnadd" class="submitlogin" type="submit">
                    </form>
				<?}else{?>
                	<p>Hi! <br><u><? echo $_SESSION[username] ?></u>!</p>
                    <ul>
                    	<li><div class="label">Silk balance:</div><div class="label2"><? echo $silk; ?></div></li>
                        <li><a href="?page=logout" id="login1_logout" class="logout">Logout</a></li>
                    </ul>
				<?}?>

$user = $_POST['TB_User'];
$pass = $_POST['password'];
$lmd5 = md5($_POST['password']);

$select_silk = mssql_query("SELECT * FROM SK_Silk");
$silk_count = mssql_fetch_array($select_silk);
$silk = $silk_count[silk];
$logcheckif = mssql_query("SELECT * FROM users where id='$TB_User'");
$logcheck = mssql_num_rows($logcheckif);
$pwcheckif = mssql_query("SELECT * FROM users where id='$TB_User' and password='$lmd5'");
$pwcheck = mssql_num_rows($pwcheckif);