It sounds like you have a bake element that needs to to be replaced. The following link explains how to access and replace one:
http://www.fixya.com/support/r3575810-replacing_the_bake_or_broil_element_in_a
It is common for the bake element to wear out more frequently than the broil element due to the frequency of use. These elements are not interchangeable because of different wattage ratings. You should also check the wiring connections between the element and the Electronic Oven Control (EOC) board. The EOC controls all the oven features. There is a separate relay on the board for each oven feature. It is possible for the bake relay to go bad, or the interconnecting wiring to the element, so you will need to check these items if your existing element checks good.
CAUTION: Make sure you follow all safety precautions and DO NOT attempt to service your range while it is still plugged in. High voltage potentials are still present in the back of the range even when the oven is not on. Always UNPLUG before taking any resistance readings.
Replacement parts can be purchased at any of the following websites:
searspartrsdirect.com
pcappliancerepair.com
appliancepartspros.com
repairclinic.com
Prices vary between sites, so shop and compare. The first three sites listed also have helpful exploded view parts illustrations to assist you with locating and properly identifying the parts you may need.
If you have any questions about this repair, or need additional assistance, please post back and let me know. I hope this helps you.