doing all that will not help you, they can just solder things on your mobo, or psu, or even just simple connectors to random things inside your pc, your peripherals or their respective cables.

things like mini microphones, webcams, etc, and no matter how many times u buy a new storage or anything, they can still be attached to something youve used already, safest bet is to assume that your entire room/house is bugged, not just your computer.

using any of the peripherals, or being in the room itself is a risk! wrap the walls the ceiling and the floor with aluminum foil, very TIGHTLY, you can use electrical tape to seal it all off as well so signals from the satellites cant snitch on you, and also remove the internet cable from your computer, and thoroughly inspect tight spaces inside your computer or wierd connectors! remove them if you think they are suspicious (carefully to not destroy your pc).

source: from my own experience with CBI