You shouldn't do anything right now. You should wait for the user to respond to you, e.g. if he needs more clarification or doesn't know how to solve his problem with your answer.
Regardless, there's no obligation for people to accept answers. Posting comments like, "Please accept my answer" are noise and – when it comes down to it – quite rude. You can ask the OP if he needs more help or if something was unclear with your answer, offering to improve it and add information.
Eventually, a "0% accept rate" shown for this OP will get him the usual "y u no accept answers?" comments from the community, so sooner or later they'll probably follow up on their questions and accept answers.
But even then, if it doesn't happen, don't worry. Two upvotes weigh more than the score you get from an accepted answer.