Initial Problem:

A user has several BSODs on his computer after it's loading.The error message is next "DRIVER_IRQL_NOT_LESS_OR_EQUAL ... ". Bluescreens on NT-based Windows systems are usually caused by poorly-written device drivers or malfunctioning hardware. In the Win9x era, incompatible DLLs or bugs in the kernel of the operating system could also cause bluescreens. They can also be caused by physical faults such as faulty memory, power supplies, overheating of computer components, or hardware running beyond its specification limits.

Troubleshooting process:

1. At first user was suggested to delete some registry enties and install winodws update, namely KB953026. The same problem still was shown on PC.

2. Disabling start up items also didn't resolve the problem.

3. After some investigation was found that problem with BSOD windows could be related to graphic card drivers. Reinstalling drivers with the newest also didn't resolve problem.

 Solution:

The last suggestion was to reinstall Windows completly.
Afer providing user with detailed instructions on how to reinstall Windows Vista, problem has gone.