title: Magento website suddenly has 'No data received' Error code: ERR_EMPTY_RESPONSE
body: <p>We have Magento running on an eCommerce website an the last few days it seems that some really important pages are simply not loading!</p>
  
  <p>Majority of the pageson the site load fine however if a user is "logged in" and they try to access the cart checkout page, by far the most important page, they receive this very nasty message shown below in the image...</p>
  
  <p><img src="https://i.stack.imgur.com/pMO0K.png" alt="enter image description here"></p>
  
  <p>As far as I know, no changes to code have been made the last few days so I do not even know where to look at this point for a solution.  </p>
  
  <p>A Google search shows that many people had had this problem before, mostly on WOrdPress sites but there never is a solution posted!</p>
  
  <p>I am hoping someone can point us in the right direction as this is a major problem on this site right now if a user cannot checkout.</p>
  
  <p>The other page that i noticed it is happening on is the page to create a new user account, once you fill the form out and hit submit, it shows the page shown in image as well.</p>
  
  <p>We are running Apache on Ubuntu 12  believe.  We also have Varnish Cache if that means anything.  </p>
  
  <p>Please help!</p>
  
  <p>Also here is what I get for the same page in FireFox...</p>
  
  <p><img src="https://i.stack.imgur.com/TyX9J.png" alt="enter image description here"></p>