The dreaded internal server error

Hi… I’ve tried looking this up and most of the comments refer to permalinks that don’t work and get this error, however not to my specific problem.
I set up a blog on a friends site for him and all has been working fine until the host changed their servers around a couple days ago. Whenever we try to go to the address for his blog (whoisthomas.com/blog) we get the 505.
I have checked the error logs on his site and I get:
[Thu Jun 3 02:29:45 2004] [error] [client 66.196.90.187] File does not exist: /home/whoist2/public_html/404.shtml
[Thu Jun 3 02:29:45 2004] [error] [client 66.196.90.187] File does not exist: /home/whoist2/public_html/robots.txt
[Wed Jun 2 23:04:06 2004] [error] [client 68.184.215.63] File does not exist: /home/whoist2/public_html/500.shtml
[Wed Jun 2 23:04:06 2004] [error] [client 68.184.215.63] Premature end of script headers: /home/whoist2/public_html/blog/index.php
Now, I am extremely new to WordPress and to php. The main reason why I installed it is because it was easy enough for a very un-tech-savvy person such as myself to run a blog (and pray that nothing goes wrong with it). I can get into the backend of Thomas’s site, I can log in and out and fiddle from there, but I am completely stumped as to how to get his blog to display as it was. Any ideas? I’m hoping the fix will be simple..