I have a Kenmore mElite Smartheat 9 gas dryer.
It was working no problem yesterday morning. In the afternoon, it still tumbled, but no heat was produced.

Here are some manuals: https://dl.dropbox.com/u/8010163/Whirlpool%20Dryers.zip
These driers will do that when the lint builds up like concrete on the inside of the air ducts. The sensors get blocked from sensing when the dryer is dirty. Halfway cleaning it will not work because all it takes is one clogged up air passage or dirty sensor. You need to totally tear it down and scrape out and wash all of the parts except the motor, which you vacuum out. You can go to YouTube to see videos on how to take it apart, but do a very good job or it will fail again quickly. I would get a new belt and change it while you have it apart and get some white lithium grease and grease any bearings you find. You need to clean out a drier every two years, at least, according to the manual. You just unplug the wires from the sensors and remove ductwork that they are attached on and clean the entire thing with soap and water. Make sure you go all through the dryer and get all parts like the blower fan and housing (it has to be scrubbed and washed out), vacuum out motor well and clean exhaust. Mark all wires you unplug so you know where they go. This is an easier job than you would think. My sister does hers at least once a year since she has five children and the dryer gets a lot of use. Make sure to clean around all of the sensors, and you can check them with a meter and the chart in one of the manuals, too. See: Dryer vent cleaning prevents fires - YouTube and: Cleaning out a dryer with top lint cleanout - YouTube
Cleaning out a dryer: By a woman 2 of 2 - YouTube You will find that one of the safeties is blown open, so you will need a meter to find which one is bad. These have to be replaced because they are non-resettable. You can buy ones that you can reset; they have a little red button on them that you push in to reset when you clean it out again.