function checkTextField(field) {

if (field.value == '') {

alert("Field is empty");

}

<title>Signup</title>

<meta name="description" content="website description" />

<meta name="keywords" content="website keywords, website keywords" />

<meta http-equiv="content-type" content="text/html; charset=windows-1252" />

<link rel="stylesheet" type="text/css" href="style/style.css" />

<div id="main">

<div id="header">

<div id="logo">

<div id="logo_text">

<!-- class="logo_colour", allows you to change the colour of the text -->

<h1><a href="index.html">Open Source Survey<span class="logo_colour">System</span></a></h1>

<h2>By Software Developer</h2>

</div>

</div>

<div id="menubar">

<ul id="menu">

<!-- put class="selected" in the li tag for the selected page - to highlight which page you're on -->

<li class="selected"><a href="index.html">Home</a></li>

<li><a href="examples.html">Examples</a></li>

<li><a href="contact.html">Contact Us</a></li>

</ul>

</div>

</div>

<div id="content_header"></div>

<div id="site_content">

<div class="sidebar">

<!-- insert your sidebar items here -->

<h3>Latest News</h3>

<h4>Red Hat Enterprise Linux 6.5 arrives</h4>

<h5>November 21, 2013</h5>

<p>Red Hat's newest update for its flagship enterprise Linux, Red Hat Enterprise Linux 6.5, is ready to go.<br/><a href="http://www.zdnet.com/red-hat-enterprise-linux-6-5-arrives-7000023500/">Read more</a></p>

<p></p>

<h4>Will a shot of Android be enough to save BlackBerry?</h4>

<h5>November 19, 2013 </h5>

<p>BlackBerry is a sick company. Will a dose of Android apps give it a shot at health?<br/><a href="http://www.zdnet.com/will-a-shot-of-android-be-enough-to-save-blackberry-7000023331/">Read more</a></p>

</div>

<div id="content">

<!-- insert the page content here -->

<form name="form1" method="post" action="SignUp.php">

<h2>Signup</h2>

<form id="searchform" method="get" action="SignUp.php" onsubmit="return checkvalue(this)">

<table cellspacing="0" cellpadding="0" width="100%">

<tr>

<td>

<h4> User Name <h4>

</td>

<td>

<input type="text" name="myusername" id="s" size="15" value="" onblur="checkTextField(this);"/>

</td>

</tr>

<tr>

<td>

<h4> Password <h4>

</td>

<td>

<input type="Password" name="mypassword" id="s" size="15" value="" onblur="checkTextField(this);"/>

</td>

</tr>

<tr>

<td>

<h4> Re-Password<h4>

</td>

<td>

<input type="Password" name="mypassword2" id="s" size="15" value=""onblur="checkTextField(this);" />

</td>

<tr>

<td>

<h4> EmailId<h4>

</td>

<td>

<input type="text" name="EmailId" id="s" size="15" value="" onblur="checkTextField(this);"/>

</td>

</tr>

</tr>

<tr align="center">

<td colspan="2">

<button >Submit</button>

</td>

</tr>

</table>

</form>

<div id="content_footer"></div>

<div id="footer">

Copyright &copy; simplestyle_1 | <a href="http://validator.w3.org/check?uri=referer">HTML5</a> | <a href="http://jigsaw.w3.org/css-validator/check/referer">CSS</a> | <a href="http://www.html5webtemplates.co.uk">design from HTML5webtemplates.co.uk</a>

</div>

</div>