Site wrecked after 'auto update' of the database 3.4.2

Hi all,

I’ve browsed a few forums and found a few answers, but none of them has worked up to now, so I’ll just ask if anyone has a better solution than a re-install of WP before I resort to that.

The situation is the following.
I upgraded my WP to 3.4.2 a few days ago, and it went smooth as silk, a 20 sec operation.
After that, I accessed both the front and the back-end of the site, but didn’t install any new plugins, nor did any major modifications.

This afternoon, as I open the webpage, I get a message: “You need to update your database” with a big “Update” button underneath. That’s surprising, I thought, since I’ve upgraded a few days ago already, but anyway, why not?
So I press the “Update” button. It tells me “Update successful!” and brings me back to the site.
AND EVERYTHING IS BROKEN!!! aAarrrahhhhgh

The homepage still displays, but all plugins seem to be failing. Can’t access any other page (get 404 error messages). Looks like permalinks are in trouble again, so I revert my .htaccess file to a previously working version — no joy.
So I try disabling all plugins, but here comes the White Screen of Death when I try accessing the Dashboard. (terror pulses through my veins)
So I FTP my way to the plugins folder, and rename it to Plugins.hold.

Nothing new.

I change the name of my theme folder to sth else —

Nothing new.

Now this is a bit embarassing.
Is there anything else I could try to fix this, apart from re-installing?

Desperately,
D-