Try holding down the left-most softkey while turning the unit on. Keep holding it down (release the power button when it turns on) the until the countdown reboots the processor. That might fix it.
Thanks Boomer, I’ll try that tomorrow. I had a problem with not getting enough gps satellites aquifer, and I found out by a google search that the rs125 unit had an internal battery (not mentioned in the owners manual). So I put in a new battery and turned it on to the blank/grey screen.
The RS125 is a separate unit providing GPS via NMEA/Seatalk. Unless you managed to short out the cabling somehow it doesn't seem like that would affect the chart plotter.
A factory reset could be in order for that C70. But understand that would lose any tracks or other data stored.
This seems to show the same problem you've got:
This point in the video mentions the common reason: