Oven won't work

I cannot get my oven to heat. The broiler works fine, and so do the top burners. What are my possible problems.

My daughter is having the same problem with her Kenmore gas range. Burners work, broiler lights and works. Oven does nothing. When you try to turn it on it displays PRE HEAT but never lights. Could it be the igniter? How do you tell if they are bad?