Meltdown – One by one things stop working – Help…!

1. The first thing I noticed was that neither Categories nor Tags were showing up at posts; all posts suddenly had become “Uncategorized”.
2. Then I saw that under the tab Categories and “Post Tags” under “Posts” all Categories and Tags had disappeared, yet it was impossible to make new Categories or Tags with previously used names, because those were already in use…
3. Then I noticed that the “automatic” way of uploading and installing Plugins no longer worked, and neither does the delete function of Plugins. The error messages usually have something to do with directories not existing, or directories not traceable (they are REALLY there, though….)
4. Then I noticed that the automatic uploading of pictures through both the Flash Uploader as well as the Browser uploader no longer function.

These errors came into existence today – yesterday everything worked perfect. I haven’t touched any of my settings.

I have taken off all plugins, but all errors remain.

I have re-installed everything APART from my database.

What on earth could cause these all these simultaneous problems?

Anyone any clue? I’m desperate…

Thanks!