The apache logs are certainly the most useful, but a profile might shed some additional light (you could be out of space for example). Can you PM me your Profile? You can download it by going to Admin > System Config > System Profile and click the ***Download Profile*** button towards the top. If for whatever reason you *cannot* download the profile, please put the output of View System Info (5.3.4+, Show Profile if older) in the thread (that will at least get us some info). This will give us access to many of the logs we would otherwise ask for individually. If security is a concern, you can unzip the profile take out what you like, and then zip it up again. We may end up needing something you remove, but we can ask for that specifically.
After you PM the profile, please update this thread. Updating this thread is the only way for it to show back up on our dashboard.