Worst case scenario: head gasket blew either because of overheating or the other way around; gasket blew and caused overheat from loss of coolant and engine is seized from coolant in combustion chamber, may have ran for a while then when both valves are closed and coolant got in. Now the good news, just fill up radiator, make sure battery is good and terminals clean, no corrosion and see if it will start, it may be fine. If it still does not start, after you KNOW the battery is good, and starter is good, solenoid good, begin pulling spark plugs one at a time and check for coolant inside cylinder, Stick a screwdriver or something inside like a dipstick, a wooden stick would be better, to see coolant if it's in there. I hope not and with any luck, after filling radiator and checking battery it will run fine.