Brush will only run for a few seconds Riccar RAD.1

SOURCE: Riccar 8800 belt replaced but now floor brush won't spin

Are you sure that you get the right sized belt? This is the correct one you need:

Riccar 8800 Belt

SOURCE: riccar model rad.7 upright (radiance). roller

As you already know, the red brush indicator light indicates that the brush roll has stopped turning, usually because an object has become stuck in the brush roll. When that happens you should turn the machine off (unplug it also for safety), remove the obstruction and turn the vac back on. That should have cleared the light and allowed your brush to turn again.
Occasionally, you will get debris in the brush roll end caps and the brush roll will spin slower making the sensor think there is an obstruction. You can remove the brush roll, pop the end caps off and clean out any debris to see if that helps.
If none of the above worked it is possible that the brush roll sensor is bad or the circuit board in the machine is bad. You'll need a Riccar service center for that. The good news is your Radiance has a 6 year warranty.