When I run my PC it shows an error message "IRQL_NOT_LESS_OR_EQUAL", and ask me to restart the PC . But after restarting same error appears again.

What did u do previous to this error?

What is the computer? (make/model)
Operating system?


What this is: This error occurs when a memory is being accessed in a location its not allowed to access.

COuld be a device driver, bad bios, virus scanner... etc

Try booting to the windows xp cd and doing a repair.

How to Perform a Windows XP Repair Install (http://www.michaelstevenstech.com/XPrepairinstall.htm)
It takes a while.. but usually works.