Its the free fall sensor, install this: [URL]
I have a dell Alienware M14x.  I recently installed windows 8.1 (new install with new HDD).  Viewing device manager, i have a unknown device error "PCI Express Root Complex" and i am unable to locate the drivers.  Can you assist me? Device type:  other devicesManufacturer: UnknownLocation:   PCI Express Root ComplexValue: ACPI\SMO8800\1IRQ  0x00000014 (20)
PCI Express Root Complex