making yogurt without yogurt maker, milk boiled when i was not paying attention, did i ruin it, still waiting for it to cool down.

I, too, neglected my milk on the stove and it boiled over (though the saucepan bottom was not 'burnt') Argh! Decided to proceed anyway. Delighted to find absolutely beautiful yogurt this morning. Thick, silky and smooth, with just a bit of tang. I’ll not be so concerned about not creeping over 190F when heating the milk.
As an aside, I always drain my yogurt, and freeze a small amount of the whey to use as the next batch's culture. Now I can eat all the yogurt I made!

yes! I've done this many times. it will work fine, assuming you add your culture AFTER it boils when it cools to the correct temp.

Probably. If the milk boiled, it might have killed off too much bacteria to culture properly. I base this theory on the fact that ultra-pasteurized milk is not recommended for making yogurt or cheese. UP milk has been heated to a high temperature to extend its shelf life. It can result in a very runny yogurt.

I would start over. Use that boiled milk for something else, like custard or ice cream.