Do you have an open array or radome? I think the radome units of that era are powered via the fat cable that also carries data but that the contemporary open array units had their own power wires, with their own fuse, and often their own power on off switch.
If it is an open array unit, I'd look for that fuse and possibly power switch
Some relatively newer digital units, open array and radome, work with those units via a Seatalk-HS. This almost always involves a SeaTalk-HS network switch that is also powered and may involve a switch or a fuse.
So, if it is digital radar, or you see a SeaTalk-HS switch, or if something like a DSM-200/300 sounder module exists but the fish finder (not simple depth) is also not working, I'd look for a switch and to see if it is powered and everything is connected.
Do you know the model numbers? The software version on the E120? If not, pictures of the units and wiring and screen may help us to help better.