well, Davis Ris, all I can recommend for now is that if you have access to another Mac or even a PC and you have a USB flash or thumb drive of at least 8 gig size/capacity, that you try to make a boot-able Mac USB flash drive. There are various utilities on the Mac side of things, eg DiskMaker X, etc, and there might be a few on the PC side.... but then again, I've never tried to make a boot-able Mac USB flash drive on a PC, but I've been told that is is possible..... you may wish to boot up, holding down the "D" key for Apple Diagnostics which should run some basic tests..... you should also try resetting the smc/pmu and zapping the pram as well....before trying recovery mode. Also, there's a pram battery behind the graphics card......it's a little button cell. It's a CR-2032/BR-2032 battery and it goes in plus side up. these batteries do fail after about 5 years, it's a bit of a crap-shoot, but if you have a dead pram battery, it may affect startup....... a new battery is about $6,, so it's worth a try..... I hate to say it, David Ris, but SSD's and hard drives can and do fail without warning..... here's how to create a boot-able Mac High Sierra USB drive, on the Mac side of things:https://support.apple.com/en-us/HT201372, or you could, if you had a DVD of Snow Leopard, start up from that and do a clean install over top of High Sierra.... I don't know if you have a DVD of Snow Leopard or not... and a working DVD drive . but if you did, you'd restart, holding down the "C" key on the keyboard....the tray would come out, and you'd put the Snow Leopard dvd in the tray label side up and then close the drawer, then immediately hold down the "Option" key or keep holding down the "C" key.....and hopefully it would start up into Snow Leopard......
just a guess though
john b