Problem with the accelerometer

Hi, first of all: my Arduino Micro bord works fine with all Funktion except the accelerometer function.

Everytime I start my Windows 7, the X- and Y-Axis shows 44% instead 50% (in DIVIEW)

Only when I press the reset button on the board or unplug the USB Cable and plug it in again, the accelerometer axis adjust to 50%.

What can I do the the Arduino adust correctly after Win7 boot?