Update: I have now added Part 3 - where I cover enabling the Driver Verifier tool. This can be handy if you are getting STOP 0xA crashes, but the faulting stack is different/corrupt each time.

Update 2: If you are getting random STOP numbers each time your machine blue screens (e.g. the bugcheck is different each time), then it's possible that your machine has a hardware issue. Do some basic hardware troubleshooting first (e.g. run a memory tester application, remove unnecessary peripherals etc)

In Part 1 we looked at common causes for IRQL_NOT_LESS_OR_EQUAL BSODs. If you end up in the unfortunate situation where you are experiencing a STOP 0XA BSODs, what can you do about it?

If you'd like to confirm the actual STOP error you are getting visually, then you need to change a setting in Windows XP and Windows Server 2003. By default the system automatically restarts upon a BSOD and you may miss the information that's printed on the screen. To view the actual BSOD use the System Control Panel -> Advanced Tab -> Startup and Recovery Settings  button -> uncheck Automatically Restart on System Failure. The System control panel is available in the Control Panel folder, or by right-clicking on My Computer and choosing Properties.

To determine what is causing the problem we want to use a debugging tool such as WinDBG. WinDBG is available for free as part of the Debugging Tools for Windows. There are separate downloads for x32 and x64 systems.

After downloading and installing the Debugging Tools start WinDBG. Press Ctrl+D to open a crash dump, and navigate to %systemroot%\minidump (%systemroot% is where your Windows/WINNT folder is located). Each time Windows has crashed, there should be a minidump file there (by default). Open the minidump file that corresponds to your crash.

Ensure that your system has access to the internet (in particular the Microsoft Public Symbol Server) and type in the following commands at the kd> prompt:
.symfix
.reload
kb

After hitting .reload, it may take some time for WinDBG to download the corresponding symbols that match the dump file (depending on your internet connection speed). These symbols allow you to see what functions are being called within files supplied by Microsoft (for third party files, you need to get symbols from those vendors. You can supply your own symbols for you own code). Because the offsets for functions potentially change with each update to Windows (service packs, hotfixes etc) being able to contact the public symbol server allows you to get the correct symbols that match the exact build in the dump file.

The kb command allows you to get a stack backtrace of the faulting thread. In most cases you can get a faulting driver from the stack. The stack should be read from the bottom up. Here is an example:

STACK_TEXT: 
WARNING: Stack unwind information not available. Following frames may be wrong.
8055052c f94c7ef9 81ae08d8 6600a8c0 6500a8c0 A3AB+0x15d90  <== Our culprit
8055058c f94c7b19 f9722404 819ab000 818a0ef0 tcpip!DeliverToUser+0x18e
80550608 f94c780a f97307a0 818a0ef0 00000054 tcpip!DeliverToUserEx+0x95f
805506d0 f988bf7f 81b184d8 fff0bdc0 ffffffff tcpip!IPRcvPacket+0x6a0
805506f8 f987354b 81b184d8 00000064 819ae0d8 NDIS!NdisMSetTimer+0x8b
8055070c f96fdd98 81b184d8 00000064 819ab000 NDIS!NdisSetTimer+0x44
80550764 804dcaad 81b18500 81b184d8 00000283 A3AB+0x2fd98
80550880 805508ac 81a915f4 804e4fd5 81aa39c0 nt!KiTimerListExpire+0x122
80550890 f988f712 00000000 80559580 80559320 nt!KiDoubleFaultStack+0x2d2c
805508ac 804dc179 81a91608 81a915f4 00000000 NDIS!ndisMDpc+0xff
805508d0 804dc0ed 00000000 0000000e 00000000 nt!KiRetireDpcList+0x46
805508d4 00000000 0000000e 00000000 00000000 nt!KiIdleLoop+0x26

The faulting driver isnt always at the top of the stack, but it's generally easy to spot. In this case, a quick search for a3ab.sys lead us to the driver that needs updating (it was for a network card).

Additional information about the modules loaded can be obtained by using the lmv command at the kd> prompt. In this dump file:

f96b7000 f96cd680   ndiswan    (deferred)            
    Mapped memory image file: ndiswan.sys\41107EC616680\ndiswan.sys
    Image path: ndiswan.sys
    Image name: ndiswan.sys
    Timestamp:        Wed Aug 04 16:14:30 2004 (41107EC6)
    CheckSum:         00016813
    ImageSize:        00016680
    File version:     5.1.2600.2180
    Product version:  5.1.2600.2180
    File flags:       0 (Mask 3F)
    File OS:          40004 NT Win32
    File type:        3.6 Driver
    File date:        00000000.00000000
    Translations:     0409.04b0
    CompanyName:      Microsoft Corporation
    ProductName:      Microsoft® Windows® Operating System
    InternalName:     NDISWAN.SYS
    OriginalFilename: NDISWAN.SYS
    ProductVersion:   5.1.2600.2180
    FileVersion:      5.1.2600.2180 (xpsp_sp2_rtm.040803-2158)
    FileDescription:  MS PPP Framing Driver (Strong Encryption)
    LegalCopyright:   © Microsoft Corporation. All rights reserved.
f96ce000 f973bf60   A3AB     T (no symbols)          
    Loaded symbol image file: A3AB.sys
    Image path: A3AB.sys
    Image name: A3AB.sys
    Timestamp:        Wed Mar 23 14:17:32 2005 (4240DFCC)
    CheckSum:         00072B2D
    ImageSize:        0006DF60
    Translations:     0000.04b0 0000.04e0 0409.04b0 0409.04e0
f973c000 f975ee80   USBPORT    (deferred)            
    Mapped memory image file: USBPORT.SYS\41107D6222e80\USBPORT.SYS
    Image path: USBPORT.SYS
    Image name: USBPORT.SYS
    Timestamp:        Wed Aug 04 16:08:34 2004 (41107D62)
    CheckSum:         0002F594
    ImageSize:        00022E80
    File version:     5.1.2600.2180
    Product version:  5.1.2600.2180
    File flags:       0 (Mask 3F)
    File OS:          40004 NT Win32
    File type:        2.0 Dll
    File date:        00000000.00000000
    Translations:     0409.04b0
    CompanyName:      Microsoft Corporation
    ProductName:      Microsoft® Windows® Operating System
    InternalName:     usbport.sys
    OriginalFilename: usbport.sys
    ProductVersion:   5.1.2600.2180
    FileVersion:      5.1.2600.2180 (xpsp_sp2_rtm.040803-2158)
    FileDescription:  USB 1.1 & 2.0 Port Driver
    LegalCopyright:   © Microsoft Corporation. All rights reserved.

Happy debugging!

Edit: Forgot my references! Other than sites that I've listed previously, the following documents have been used:
IRQL and Scheduling Whitepaper from Microsoft and
Windows Internals by Mark Russinovich and David Solomon