My electric oven takes a long time to preheat and will only reach a temperature of 340.
Here are your parts
http://www.appliancepartspros.com/partsearch/modelsearch.aspx?model=790.97479800
Here is the tech sheet
http://manuals.frigidaire.com/prodinfo_pdf/Springfield/316519953.pdf
"Oven will not heat" and "oven takes a long time to preheat and will only reach a temperature of 340." so I am not sure if it is getting any heat at all.
If you go to the Sears parts site they should have actual part breakdown diagrams. Unfortunately they do not like to share theses with other parts sellers.
Does the unit come ready or stay in preheat?
If it comes ready then it could be an oven sensor problem.
If it stays in preheat do both elements work?
On most units the oven switches back and forth between the bake and broil elements. Also does this during bake.
Check the elements.