Well, it is very possible that one of your drivers doesn't comply with the Advanced Configuration and Power Interface (ACPI) standard for power management... due to the little info that you give, i cannot directly help you... but you can learn to use the Microsoft Debugging Tools...

read the first post at http://forums.majorgeeks.com/showthread.php?t=35246 ... 

at your next BSOC, reboot and run the bugcheck...

for example ( from laptop with Vista ) :

0: kd> !analyze -v
*******************************************************************************
*                                                                             *
*                        Bugcheck Analysis                                    *
*                                                                             *
*******************************************************************************

DRIVER_POWER_STATE_FAILURE (9f)
A driver is causing an inconsistent power state.
Arguments:
Arg1: 0000000000000003, A device object has been blocking an Irp for too long a time
Arg2: fffffa80048ec060, Physical Device Object of the stack
Arg3: fffff800045fd518, Functional Device Object of the stack
Arg4: fffffa80043815f0, The blocked IRP

Debugging Details:
------------------

DRVPOWERSTATE_SUBCODE:  3

IMAGE_NAME:  pci.sys

DEBUG_FLR_IMAGE_TIMESTAMP:  4a5bc117

MODULE_NAME: pci

FAULTING_MODULE: fffff88000f78000 pci

CUSTOMER_CRASH_COUNT:  1

DEFAULT_BUCKET_ID:  VISTA_DRIVER_FAULT

BUGCHECK_STR:  0x9F

PROCESS_NAME:  System

CURRENT_IRQL:  2

STACK_TEXT: 
fffff800`045fd4c8 fffff800`030f6e23 : 00000000`0000009f 00000000`00000003 fffffa80`048ec060 fffff800`045fd518 : nt!KeBugCheckEx
fffff800`045fd4d0 fffff800`03093fa6 : fffff800`045fd618 fffff800`045fd618 00000000`00000007 00000000`00000000 : nt! ?? ::FNODOBFM::`string'+0x29330
fffff800`045fd570 fffff800`03093326 : fffffa80`0959f168 fffffa80`0959f168 00000000`00000000 00000000`00000000 : nt!KiProcessTimerDpcTable+0x66
fffff800`045fd5e0 fffff800`03093e7e : 000000b9`fff258c5 fffff800`045fdc58 00000000`004e2373 fffff800`032040e8 : nt!KiProcessExpiredTimerList+0xc6
fffff800`045fdc30 fffff800`03093697 : 00000030`510838ce 00000030`004e2373 00000030`510838d4 00000000`00000073 : nt!KiTimerExpiration+0x1be
fffff800`045fdcd0 fffff800`030906fa : fffff800`03200e80 fffff800`0320ec40 00000000`00000001 fffff880`00000000 : nt!KiRetireDpcList+0x277
fffff800`045fdd80 00000000`00000000 : fffff800`045fe000 fffff800`045f8000 fffff800`045fdd40 00000000`00000000 : nt!KiIdleLoop+0x5a

STACK_COMMAND:  kb

FOLLOWUP_NAME:  MachineOwner

FAILURE_BUCKET_ID:  X64_0x9F_3_NETw5s64_IMAGE_pci.sys

BUCKET_ID:  X64_0x9F_3_NETw5s64_IMAGE_pci.sys

Followup: MachineOwner
---------

In these example, the bugcheck analysis points to the NETw5s64.sys, which is a driver for Intel wireless.

Check to be sure your computer and all devices are on the Hardware Compatibility List (HCL) and have WHQL signed and certified drivers. You can use Sigverif.exe to check for unsigned drivers.

Check software that uses filter drivers ( for example, anti-virus, remote control, and backup software ).

The best way is to debug yourself... Installing the Microsoft debug tool can seem a little complex but it need to be done one time only... can be very useful because all the driver are not certified, specially the beta version...