Error MessageWarning: require(includes/application_top.php) [function.require]: faile

I have read a few posts and tried changing permissions. to 755 etcI am using Zencart 1.38. It happened when I tried to change hosts. I am now still with the original and the site is giving the above error message. I have a backup on my harddrive and I am using FileZila. Can I just upload it all back again over the previous or do I have to try something else?
What else can I try please if the above is not going to work?

Update, I now have a login page when I point to my domain via web, but when I login, nothing happens. Login page disappears. This is the first login page, prior to the problems, a second screen would come up. Still no sign of site content. :dontgetit

Several things:

1. Get a clean install of ZC working on the new server first. Use the same ZC version as you've got on the old server.

2. Then bring your old stuff over.
   There's an FAQ article which explains the process: https://www.zen-cart.com/tutorials/index.php?article=100

3. Then, once it's working there, upgrade to the latest ZC version. Your version is obsolete.