BSOD BSCode 0x0000009f at Random times of the day. DRIVER_POWER_STATE_

Every couple of hours, my computer just shuts down with the BSOD. I'm not sure why. It seems like there may be a driver problem or something. See below for mini-dump) I have also attached the dump and event information for your perusal I would love to get someone to help me fiture out what the problem is. Thanks.
rmyabuki

Dump File : 112211-40466-01.dmp
Crash Time : 11/22/2011 2:33:45 AM
Bug Check String : DRIVER_POWER_STATE_FAILURE
Bug Check Code : 0x0000009f
Parameter 1 : 00000000`00000003
Parameter 2 : fffffa80`07b04680
Parameter 3 : fffff800`00b9c3d8
Parameter 4 : fffffa80`11a28010
Caused By Driver : ntoskrnl.exe
Caused By Address : ntoskrnl.exe+7cc40
File Description : NT Kernel & System
Product Name : Microsoft® Windows® Operating System
Company : Microsoft Corporation
File Version : 6.1.7601.17640 (win7sp1_gdr.110622-1506)
Processor : x64
Crash Address : ntoskrnl.exe+7cc40
Stack Address 1 :
Stack Address 2 :
Stack Address 3 :
Computer Name :
Full Path : C:\Windows\Minidump\112211-40466-01.dmp
Processors Count : 4
Major Version : 15
Minor Version : 7601
Dump File Size : 818,424
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OS Windows 7 Professional x64 CPU Intel Core i5-2500k Motherboard MSI P67A-C43 (B3) Memory 8G DDR3 99924, Dual Channel Graphics Card(s) NVIDIA GeForce 9500 GT

Hello rmyabuki & welcome!

Analyses
Your atapi-driver was included in this bunch of dumps, and that's a Windows Update driver so the first thing you want to do is to run a command. Do it this way:

i) Search for 'cmd' in your rb:
ii) Right click it and run it as administrator
iii) Type 'sfc /scannow' and hit enter
iv) It might not find anything, so be sure to run it 3, 4 times

Bugcheck

Fred.