How does writing stuff off for a business work?

So, I run a small business-ish operation where I repair computers, and go out on service calls and whatnot, although the name isn’t trademarked or registered or anything.

I find myself in need of a new desktop PC, my old xps 720 is getting old, is kind of unstable and can’t do as much as an i5 or i7 would be able to, even with a fairly expensive video card a lot of games and programs slow down because of the CPU, I especially notice this when rendering.

I was sort of wondering, would it be possible to build a PC and write off the cost somehow? I do use it for the business, running VMs and getting familiar with different operating systems, but I don’t know the start of dealing with this sort of thing, or if writing of a PC that cost ~2k would even work.

I am thinking of this because it would be pretty nice to be able to build a good gaming and multi purpose rig and do it for (from what I understand) free. I’m sure other people have thought of this before though and it could count as fraud, not sure the exact rules around it though.

Note that I am in Canada not the US, if that makes a difference.