My hibiscus shrub has lots of buds, but the flowers are opening slightly then dying off.
Have you checked to see if Japanese beetles are eating the flowers before they have a chance to bloom fully? If you do find beetles, use Sevin dust or spray to kill and discourage the beetles. Since beetles live in the ground around the roots of the plants they eat, rake through the soil and add the Sevin dust and then rake it into the soil. It also is possible to spray the soil and then rake in the soil saturated with the spray.
You might check to see if the shrub is receiving enough light and the right amount of water to bloom properly.