Updated WordPress and Lost Site

This must be the worst New Year ever! In a fit of optimism and resolutions to stay up-to-date, I tried to update all my plugins and the version of WordPress I am using.
Rather stupidly, I also tried to update WordPress without first disabling plugins. Yes, I know, I’m an idiot, but everyone makes mistakes!
The net result is that the website (www.phillipdonnelly.net/blog) is dead. I can’t even access the WordPress Dashboard (www.phillipdonnelly.net/blog/wp-admin). Chrome tells me there is a “HTTP Error 500 (Internal Server Error)”.
I’ve spend the last day crawling over this and other forums and I’ve tried the following without any success:

1. Plugins–Disabling plugins by renaming them. Yahoo host the site and in their directory I changed ‘plugins’ to ‘plugins.hold’ but this had no effect. Creating an empty ‘plugins’ folder similarly achieved nothing.
2. Wp-config issue–I’ve checked the last part of my wp-config file and there is no extra space after the closing “?>”?tag
3. Themes–I changed the name of the theme (Suffusion) in an attempt to force WordPress to return to the default theme but this had no effect. I mean, the page is still dead. Changing the folder name to ‘themes.hold’ also had no effect.
4. Yahoo has a snapshots facility and I’ve changed hundreds of files back to what they were a couple of months ago but the site and the WordPress admin page is still dead.

After 8 hours of this, I’m about to throw in the towel. Is there anything else I can do?