1) Make sure the lens is clean. If not, be gentle to wipe off any dust. Scratches can also alter quality; make sure you take care of the lens.
2) Look through the settings to make sure you didn't accidentally change something important.
3) Call Sony and describe your problem. Have you checked their website for others experiencing the same problem?

You say you had acceptable results earlier, but, just to be clear, camcorders are not made to take excellent still photos. Whenever possible, use a still camera.