The Xbox kinect is a bit different from the PC version of the Kinect, it can track your movements only when you are a bit farther away from the Kinect. The PC version of the Kinect however can detect you even when you are a bit closer, so if you move back a bit, it will be able to detect you.
From Microsoft
The Kinect for Windows sensor is a fully-tested and supported Kinect
experience on Windows with features such as “near mode,” skeletal
tracking control, API improvements, and improved USB support across a
range of Windows computers and Windows-specific 10’ acoustic models.
The sensor was specifically designed to be used with computers, and
includes a shortened USB cable to ensure reliability across a broad
range of computers. Kinect for Xbox 360 was built for and tested with
the Xbox 360 only, not with any other platform, which is why it is not
licensed for general commercial use, supported, or under warranty when
used on any other platform.
Kinect for Xbox 360, on the other hand, was built for and tested with
the Xbox 360 only, not with any other platform, which is why it is not
licensed for general commercial use, supported, or under warranty when
used on any other platform.
Microsoft has a large team of engineers that is dedicated to continual
improvements of the hardware and software associated with Kinect for
Windows, and is committed to providing ongoing access to Microsoft's
deep investment in human tracking and speech recognition.