Why my xbox one sensor is not sensing people

There are several things that you can do:

1. Start by making sure that all of the lenses are clean on the Kinect sensor bar. Use a soft microfibre cloth and use a polishing motion. On the IR sensor (the one that doesn't look like a normal camera), you may want to use a small amount of glass cleaner, but just use a little bit of water on the cloth to clean. There should barely be water, just enough to loosen dirt.

2. If the console itself is dusty, it may be thermal throttling to protect itself. Use the Xbox One Fan Replacement guide to remove the dust. Don't remove the heatsink unless you have additional thermal paste to reapply, and you know how to reapply the goop. Use a can of air to blow out the dust in a static-free environment. NEVER use a vacuum, as this can cause static buildup and zap your stuff. (Static electricity is bad for electronics).

What is thermal throttling? Modern processors create massive amounts of heat, especially when they're under load. Computers, like consoles, have coolers on these processors to protect them and keep them from burning up and damaging everything or even catching fire. However, if there's something blocking to cooler from operating normally, such as dust or hair, then the processor will start heating up more than normal. To protect itself, the processor will 'throttle' its performance back to run as coolly as possible, just short of turning itself off. Once the obstructions are cleared and the processor is getting cooled adequately, it should return to its original performance.