Hello Claire - Welcome to the Sony Forums 
Have you tried doing a full reset of the camera to see if this fixes the problem? The full instructions can be found on page 119 of the manual and if you do not have it to hand, you can download a PDF version from here:
http://pdf.crse.com/manuals/4191047121.pdf
If this doesn't help, please reply and I will provide details for getting in touch with Sony Customer Services who will be able to advise you if a repair is needed.
Thanks,
Simon