Depending on what kind of board you have, after you trashed the preferences you might have to re-enable non-square (aka 720 aka 601) media in the prefs. (Some revisions had a separate 601 enabler.) That would explain the 720 slashed circle. But the error -19097 sounds ominous and so does the diagnostics failure. You could try turning off the Mac and carefully re-seating the board and connector cable. Even powering down for a while and letting things cool might help temporarily. Or of course it could all go totally bad in an instant. If things are really critical you should contact M100 and see what answers and prices they might have.