Demystifying the BSOD

Source
Anatomy of a Blue Screen
The Error Message
Modules That Have Loaded
Modules That Were About to Load
Kernel Debugger
An Easier Way
Memory Dump
Last Known Good Configuration
Conclusion
IRQL_NOT_LESS_OR_EQUAL
The IRQL_NOT_LESS_OR_EQUAL error is caused by a buggy device driver or an actual hardware conflict. If you've recently added new hardware to your system, try removing it and see if the error goes away. Likewise, if you've recently loaded a new device driver, you might try using ERD Commander Professional Edition, by Winternals Software, to temporarily disable the new driver and see if the problem goes away.
KMODE_EXCEPTION_NOT_HANDLED
An incorrectly configured device driver usually causes this type of error. As I'll explain later, you can use another section of the blue screen to figure out which driver is causing the problem.
REGISTRY_ERROR
Such an error indicates a catastrophic failure in the system's registry. However, this error can sometimes be caused by failure to read the registry from the hard disk rather than because the registry itself is corrupt. Most of the time though, if you get this error, you'll have to restore from backup.
INACCESSIBLE_BOOT_DEVICE
Just as the name implies, this error indicates that Windows NT is having trouble reading from the hard disk. This error can be caused by a faulty device driver or a bad small computer systems interface (SCSI) terminator. If you've checked for these problems, but are still receiving the error, check to make sure that a virus hasn't destroyed your boot sector.
UNEXPECTED_KERNEL_MODE_TRAP
This error message is almost always caused by your computer's memory. If you receive this error, check to make sure that all of your single inline memory modules (SIMMs) are the same type and speed. You should also check to make sure that your computer's Complementary Metal Oxide Semiconductor (CMOS) is set for the correct amount of RAM. If all of these suggestions check out, try replacing the memory in the computer.
BAD_POOL_HEADER
This is, perhaps, the most obscure error message. In most cases, if you receive this error, it's related to the most recent change you've made on your system. Try undoing the change to get rid of the error.
NTFS_FILE_SYSTEM
An NTFS_FILE_SYSTEM error indicates hard disk corruption. If your system is bootable, run CHKDSK /F on all of your partitions immediately. If your system isn't bootable, try installing a new copy of Windows NT in a different directory. You can use that copy to run the CHKDSK program. When you're done with the second copy, you can edit your BOOT.INI file to make your computer start your original copy of Windows NT.
KERNEL_DATA_INPAGE_ERROR
This error indicates that Windows NT wasn't able to read a page of kernel data from the page file. Bad memory, a bad processor, incorrectly terminated SCSI devices, or a corrupt PAGEFILE.SYS file may cause this situation. The first step in correcting such an error is to recreate the PAGEFILE.SYS file and see if you can bring your system back online.
NMI_HARDWARE_FAILURE
This is a generic error message in which the hardware abstraction layer can't report on the true cause of the error. In such a situation, Microsoft recommends calling the hardware vendor. This error can sometimes be caused by mixing parity and non-parity SIMMs, or by bad SIMMs.