It's unlikely that the yeast are dead.
From what you posted I'm assuming that you just pitched the contents of the smack pack/vial into your wort.
You didn't pitch enough yeast (I know the package says it's enough). However, it will get started, it will just take longer than you expect.
Don't know what you are fermenting in, if it's a bucket, you may have a leak around the lid which would allow CO2 to escape there versus the airlock. If it's a bucket, have you opened it to see what's happening?
Pick up a pack of US-05 and if there is still no activity after 48 hours, pitch the it.
Next time make a yeast starter.
Lot's of info here on the forum about making and using yeast starters.