You have turned on the stove burners to make sure you are getting propane thru the lines, correct?
The check valve you are referring to is most likely in the propane tank, which will shut off excess gas flow in the case of problems. Sometimes, when you open the cylinder valves too quickly, the check valve activates and shuts off or severely limits the flow of propane from the cylinder.
This is why you were advised to completely turn off the propane cylinder handle, then slowly reopen it.......to reset the check valve inside.
Make sure you have good propane flow from the stove....then move on to the water heater.
You may just have a propane problem....and thus the water heater is not getting the propane it needs for the Direct Spark Ignitor to light.
Propane 101-The basics
EDIT: Wow, I type slow. Herk added 3 more posts by the time I did my one little post. LOL