I have managed to find the main problem: bad connection of a VGA cable
(I also replaced the 13W3-VGA adapter).
Some problems still remain: the SGI Indigo has deplatted PRAM battery
(I have to replace it) and the Indigo2 HDD failed (it does not show in
the system). The SCSI is probably OK as I can connect the CD-ROM.
I should postpone the Indigo2 restoration until I will be able to get a
SCSI sled and a proper drive...
