javascript onlcik not working in my plugin

my javascipt onclick function not working in wordpress plugin.
I’m a beginner in wordpress. I read article about creating plugin for wordpress. Actually I created a simple javascipt photo gallery once & I want that in wordpress so I built wordpress plugin.Eveything works fine but when I click the next button it does nothing. This works fine in my HTML page.Why so???
Is wordpress blocking onclick function script????
although javascript alert() executes fine. Plz help me

Here my code:

<script language="javascript" type="text/javascript" src="https://localhost/wordpress/wp-content/plugins/Vishu-Gallery/script/MyScript.js"></script>
<ul id="vishuGalleryNav">
<li id="previousButton" onclick="alert(window.location)">Previous</li>
<li id="currentImage">1</li><li>of</li>
<li id="totalImages">15</li><li id="nextButton" onclick="next()">Next</li></ul></div>

This is not complete code I just pasted what I think is imp. Is anyone here solved that plz let me know.
Thanx in advance.