How can I identify the faulty part in my PC?

This will vary component by component. Usually if your computer came new from a company, then it's best to follow the manuals to attempt troubleshooting. If your computer throws an error code, try writing it down and searching the error code to find a potential fix. If your computer is refusing to boot, however, this is where things get more complicated. Certain computers usually have a built-in speaker that can perform "beep codes" to verify a fault in the system. If the computer does not beep, open up the case (doing so may void warranty, it depends on your local right-to-repair laws) and remove the RAM sticks and reinsert them one by one to ensure it is just a bad RAM stick and not a failing DIMM slot.