Here is a tip for you, when it is going to be that cold, unless you have a block heater you MUST leave the engine running.
The coolant is only rated to a freeze protection of about -40*F, any 5w-engine oil will have a flow rate rated at about -20*F.

You starved the engine of oil when you tried to start it.
No amount of engine flushes or additives will do you any good, just drive it.