Does the motor get hot? Try spinning it by hand, if it is seized up then you need a new one. Otherwise you have to check for power going to the motor. If none then you have to find out why.

Thanks for your fast reply, Baltar!

I've had some time to learn and troubleshoot, so now my question has changed.

I've tested the fan, fan switch, upper & lower switches and they test good. (I tested with a lighter and a continuity meter)

My pilot lights and stays lit, when I turn up the thermostat the burner lights.

The fire coming from the burner is not as big as I remember - nor does it make as loud of a "whoosh" sound - and its yellow flame. Isn't it supposed to be a blue flame? I'm thinking that it's not getting hot enough to trip the fan & lower limit switch.

Wow! I fixed it!

I figured the air/fuel mix was off, so I checked the air return, but it was free from obstruction. Then I finally got the nerve to take the regulator out to see if the burner tube was obstructed, but it was fine as well. I almost gave up and called a professional, but then on a whim I took a toothpick and stuck it in the regulators opening that the gas comes out of to flow through the burner. I fished out a spider nest! Now the flame is huge and blue and I'm already warm!

I have a fear of gas lines - when I was a child I was close by when a building exploded from a gas leak. This is a personal triumph, my wife can be proud!