webpage not working

hello everyone, i'm trying to design this website, i decided to put a contact us link onto my nav bar, while on the contact us page, if you click the products link the browser navigates away from the contact us page and displays the products page, but if you try navigating back to the contact us page the webpage says your file was not found, i have made sure the html file is in the html folder, i have tried launching the contact us page from the file which is working, here is a sample of my code:

<ul>
<li><a href="../html/newhome.html">Home</a>
</li>
<li><a href="../html/products.html">Products</a>
</li>
<li><a href="../html/contactpage.html">Contact us</a>
</li>
</ul>