[DVE]

Thanks all for the help, it is really useful.

I've got a serial connection to the Indigo2. It's, by the way, confusing, that on the https://wiki.preterhuman.net/SGI_Indigo2 page is written that the computer has an RS422 serial port. I've ordered an industrial RS422 to USB adapter, but it looks like the standard serial is in use, and it is not RS422, so I spent 15 Euros for nothing (not a big deal compared to the full costs anyway). Anyway, a MiniDIN-to-Serial adapter works well, I've got a PROM menu:

>> version
PROM Monitor SGI Version 5.3 Rev E IP22 Sep 28, 1995 (BE)
>> hinv -v
                  System: IP22
                Processor: 250 Mhz R4400, with FPU
    Primary I-cache size: 16 Kbytes
    Primary D-cache size: 16 Kbytes
    Secondary cache size: 2048 Kbytes
              Memory size: 64 Mbytes
                Graphics: MG10 Impact

When I select "Diagnostics", I've got something like "No partition found", so it looks, I need to connect SCSI first. I am going to use SCSI2SD and waiting for the SCSI-2 to DB25 adapter now from post. By the way, is it possible to write a full IRIX OS image to SD card using Win32Imager or a similar tool? 

As for the display, it is for me not clear, why I have a black screen. Can it be possible that my monitor is just not supporting this Green Sync mode? Or should I get at least something? VGA is an analogue signal, should I get at least blinking or something like this?