I have a "used" C720-2848 Chromebook. When the power cord is plugged into it, it flashes a white screen, then the screen goes gray, then black. Each for about three to five seconds. This goes continually, but it can be stopped by holding down ESC + Refresh + Power. I have plugged a recovery USB stick into it but cannot get it to do anything other than that same white, gray, black screens, so I cannot enter developer mode, or any other mode for that matter. I have tried all of the keystroke patterns and combinations on at least twenty different sites to try to find any mode I can work with.
Occasionally, if I haven't tried to do anything to it for a few days, I get either a Chrome OS flash on the screen, or a picture of some girl (probably a previous owner's girl). But then it goes into the same white, gray, black screens again after a few seconds.
I got an M2 - NGFF enclosure to look at the contents of the SSD. When I use a linux (Ultimate Boot CD 5.30) boot cd on my desktop, I can see the many partitions on the drive. I don't see any real OS looking files, though, just a few txt files and a log file or two. Of course, I really don't know what Chrome OS should look like, other than it is a linux clone of some nature. I can see some normal looking folders on the /dev/sdc1, 14 gig partition.
Is there anything else I can try? I hate to just give up on the thing. Without the ability to alter the strange look at boot, or change the boot device, I am stuck. Any help would be appreciated.