When ours did it we had to replace the heating element, not sure if that's the official term.

OMG call a repair service. No one on DCUM can fix your oven for you.

Could be pilot light. On my old stove the pilot light can go out.

Was it a GE?

Did you offer it a raise? Paid family leave?

Try searching google and youtube for something like "oven won't heat"

I also use the repairclinic site. Here is the link on the site for oven won't heat:
http://www.repairclinic.com/vwo8/RepairHelp/How-To-Fix-A-Range-Stove-Oven/11---/Oven-won-t-heat

I first came across the site when looking for parts for my washing machine. Home Depot partners with this site for selling appliance parts to customers. The prices are better than Sears.

But more recently I found the same parts on Amazon for cheaper so just got them from there.

If you have a gas oven, I might be more careful and go with a professional.

I don't know, but this happened to my mom, and she had to get a new oven.

In the middle of baking.

My timer went off, and when I checked the items I noticed they were half cooked and the oven was not hot, just warm.

It was working fine (preheated to correct temp, cooked a dish for about 20 minutes).

When I realized it wasn't working it was down to 220 degrees from 425.

The display is working properly.

The gas burners are working fine.

Any ideas of what it counld be? Pilot light maybe?