Dashboard trouble (WP 3.3.1 / 3.3.3)

Hi there,

I have got problems with two of my WordPress installations: In both of them, the dashboard suddenly stopped to work properly. At the beginning of the week, everything was fine. I actually didn’t do anything, but now in the dashboard, only the menu on the left is shown whereas the right “column” is empty/white. Also the menu bar is missing. This holds true for most dashboard subpages, except for some subpages of certain plugins like the Jetpack site stats which work and also show the menu bar at the top. The frontend still looks perfectly fine.

Here is a screenshot of the broken dashboard: https://www.dasgedichtblog.de/wp-content/uploads/2013/12/backend-broken.png
And, as an example, this is what the Jetpack site stats subpage looks like: https://www.dasgedichtblog.de/wp-content/uploads/2013/12/backend-ok.png

While this is an older version and the plugins aren’t the latest versions, until recently there were no problems (which means, no reason to change anything including updates).

I already:
– deactivated plugins via FTP (which, I guess, rules out plugins, be they out-dated or current versions)
– deactivated themes via FTP
– deactivated both plugins and themes via FTP
– uploaded new core files (WP 3.3.3 from the release archive; didn’t want to upgrade to 3.8 because I’m afraid it will break a lot of “small” things which would cause a lot of work – if I was sure, that the upgrade would solve it, I would do it, though), i.e. everything except for wp-content, wp-config and .htaccess
– activated debug mode (which didn’t bring up any helpful results)

All of this didn’t help at all. So, as I didn’t change anything and the same issue appeared on two WordPress installations on the same webspace (hosted by 1&1), I figured it could be related to some changes made on the server side. The support hotline, however, told me they didn’t do anything (though I’m not completely convinced that this is true).

I can’t completely rule out that the sites were hacked, but I don’t find any indicators for that, either.

Have you got any suggestions what I could try to solve the issue? Or maybe an idea what could cause such issues on the server side?