It should be the onscreen display driver see here: [URL] Try taking the Windows 8.1 driver from the M17x-R4: [URL] 
Hi All I have been having problems with an unknown device for quite some time. Just re-formatted my Alienware M17x-R3 to Windows 8 Pro, Upgraded to 8.1  (Have been running Win 8 since Beta Testing) and still have an unknown device. Id Tag details... ACPI\VEN_CPL&DEV_0002ACPI\CPL0002*CPL0002 This is a 64bit system, 16GB Ram, Intel i7-2720QM CPU, Intel HD 3000 + Nvidia GeForce GTX 460M Graphics. Hope someone can help identify this stubborn unknown  'Other devices'  issue. Thanks in Advance Roy. PS.. I am aware this laptop doesnt have support for Win 8, but it works perfectly 99% of the time, but with occasional once/twice a week Driver_Power_State_Failure crashes
Alienware M17x-R3 Drivers