tl;dr: server would not boot because of a misconfiguration originating in failed hd, Ryan saved the day. Thanks!
A while ago a hd failed on the new server already hosting the wiki, forum, explorer, etc. Because it is running on a raid system it did not really do anything. After a short while the failed disk was replaced, all fine.
But this morning the server crashed, possibly because of some experimentation. Not even the main server containing all the VMs would restart properly only some rescue mode but there was nothing in the boot logs. First it did not look so good but after some research Ryan fortunately figured out something had not been properly configured with the new disk (grub, multiboot loader). Thanks for the great work!