This server was down the first time since I have it (390 days). I had a discussion about connectivity with the host yesterday (server is having packet loss fairly often since 2 weeks now) and I suspect that someone there turned it off/on yesterday without asking me. Either that or power went off for a while.
The web server conf file wasn't set up properly (it was still using the previous conf version) so the web server couldn't start. My fault with the conf file but this long downtime wouldn't have happened if nobody other than me touched the server...