Aaargh! Why is there no consistency? So far "essaye" has been accepted three times as a correct alternative here (Yes, I have been having trouble with this lesson) and now it is incorrect and should be" essaie".
No, that's wrong. It's not at all like the "to" in "to sleep". That "to" already is part of the infinitive, "to sleep" (dormir). As dannyjmt explained, the "de" goes with the verb "essayer". It has nothing to do with dormir in this case.