Fatal Error: require

Hi,
it’s a couple of days I’ve been having problems with my website at first I saw only php code on every page. I asked my hosting and they told me I had to reset my php configuration. I did it and it worked but meanwhile, trying to solve the problem on my own, I may have made a mess with something else….

Currently I re-loaded all my website and on the home page I have these lines:

Warning: require(/home/mhd-01/www.narcononargo.it/htdocs/wp-blog-header.php): failed to open stream: No such file or directory in /home/mhd-01/www.narcononargo.it/htdocs/index.php on line 17

Fatal error: require(): Failed opening required ‘/home/mhd-01/www.narcononargo.it/htdocs/wp-blog-header.php’ (include_path=’.:/usr/share/php:/usr/share/pear’) in /home/mhd-01/www.narcononargo.it/htdocs/index.php on line 17

The file wp-blog-header.php is there and it is ok, not corrupt. I loaded a new version of WordPress and then I FTP’ed the files of my website back, so the wp files should all be OK. I tried to deactivate all the pluging and theme to see if something changed, but the error is still there. I have access to my admin area and there everything is fine…

I really don’t know what to do now!!!

Can anybody help me with this?

Thank you!!!