Hi Martin,
the HTML source code of your page does not contain the page content:
<div id="mw-content-text" lang="en" dir="ltr" class="mw-content-ltr">
<!--
NewPP limit report
Preprocessor node count: 3/1000000
Post‐expand include size: 0/2097152 bytes
Template argument size: 0/2097152 bytes
Expensive parser function count: 0/100
-->
<!-- Saved in parser cache with key db455160277:pcache:idhash:2-0!*!*!*!*!*!* and timestamp 20140311022943 -->
</div>
where there instead should be the actual content. This looks like somehow the complete page content is not rendered currently. Although you use a custom skin, this problem is also present for other skins, e.g. for Monobook. It also seems not to depend on a certain page; in my tests this is the output for all content pages.
I thought you might have wrong content in cache, but trying to clear the cache shows this: http://test.aa6e.net/wiki/Internet_Service_Providers?action=purge Also on the "purge cache" page the page "content" is missing. The same for special pages like Special:Version. Strange...
Yes, if you changed anything in the last time, try changing it back; maybe you set something, which somehow influences how content is rendered; I am not sure, if a daylight saving setting might be relevant here, though.
Maybe this is also somehow caused by the extensions in the 1.19.12 tarball, which are wrong. This should be fixed by the upcoming release of this evening.