Cart doesn't load: Internal Server Error

I have a major problem with a Zen Cart I admin. It had been working fine until yesterday when I visited the site and could only see the typical Apache 500 Internal Server Error. Actually, I was notified about the error yesterday, so it probably happend earlier. I haven't done any changes to any zen cart files/db, but other people have ftp access to all the files.

My hosting uses cpanel so I've tried to access appropiate logs to figure out exactly what causes the error, but so far, the Apache logs haven't been useful at all. Only thing that shows up in the error log is stuff like:

[Sat Aug 25 11:52:47 2007] [error] [client 11.12.13.14] File does not exist: /home/foobar/public_html/404.shtml
[Sat Aug 25 11:52:47 2007] [error] [client 11.12.13.14] File does not exist: /home/foobar/public_html/favicon.ico

I also looked at the error_log file in the Zen Cart root directory. The last data in the log file are from 21-Jul-2007 19:56:15, so it isn't really useful.

Does anyone know what's going?
Which server logs can I look at?
Is it possible that a server update by the hosting could have caused this?
Is it possible that the cart has been hacked?

I truly appreciate any help you can offer to solve this pressing issue.

thaufoo:

Only thing that shows up in the error log is stuff like:

[Sat Aug 25 11:52:47 2007] [error] [client 11.12.13.14] File does not exist: /home/foobar/public_html/404.shtml
[Sat Aug 25 11:52:47 2007] [error] [client 11.12.13.14] File does not exist: /home/foobar/public_html/favicon.ico

> 
> 
> I also looked at the error_log file in the Zen Cart root directory. The last data in the log file are from 21-Jul-2007 19:56:15, so it isn't really useful.You're right, that's not very helpful !
It's odd that the last entry was July 21. Perhaps this has been happening since then ?
Or maybe your hosting configuration has turned off error logging since that time?

> **thaufoo:**
>
> Which server logs can I look at? 
> Is it possible that a server update by the hosting could have caused this? 
> Is it possible that the cart has been hacked?Yes, both situations are possibilities.


I would treat it as though it were a hack ... audit all the files to be sure what's on the server is "expected", and remove anything not expected.  Use a procedure similar to this:
<http://www.zen-cart.com/wiki/index.php/Troubleshoot_-_Diagnosing_Obscure_Issues>

Then proceed with additional suggestions here:
<http://www.zen-cart.com/wiki/index.php/Recovering_From_Hacks>

Here's hoping you have been making good backups on a regular basis.