You have a weak or bad ignitor most likely (if it's ashy in color more then likely it's bad) Make sure you have 120v going to ignitor also if you have an amp clamp make sure your ignitor is pulling at least 3 amps if not it's bad........if you have 120v down to the ignitor and safety valve and the ignitor checks out ok it's probably the safety valve.....

Doesn't matter if it's glowing very orange it can still be bad if it's not pulling enough amps telling the safety valve to release............like i said if it's ashy when it's cool then it's probably bad that's the most common thing that goes out on ovens.........the safety valve is the small box underneath the ignitor near the floor that the burn chamber sits on it usually has 2-4 wires running to it.........go to sears parts website and look at the schematic to determine what parts are what.