If you use it daily and many hours each day it will last a year or 1? before you need to replace part/s, if your lucky you might run it for 2 years but sadly hardware are deliberately being made to last shorter so you have to buy it more often.
IF you have a watercooling system i can agree to 3-4 years but no way you will run that long with fans even if you clear dust weekly.
After 1-2 years your Graphics card wich is usually the part that needs to be replaced or Hard Drives unless the card is watercooled.
I havent used fans on hardware in my last two builds, watercooling is just so much better and easier to maintain as you dont need to dust as often and dont forget the noise.
Wrong.
No water-cooling ever yet and most of the systems I've built (all for about $1000 each time) have gone 4+ years (some closer to six) where the only thing I've replaced is the video card ... once. And even that I didn't always
have to change to play the current games, sometimes I chose to because I just wanted a new gizmo. I'm a geek like that. One time in 15+ years I had to buy a GPU twice, because it actually broke. Half my GPU's and CPU's/RAM/other parts are still used by my husband in some crap 'testing' pc's he likes to have around.
And yes, I use my PC's every day, they're on almost 24/7. When I build a new one, I keep the old one, so I always have 2 cycling. Like now, the older one is using XP for older games/programs and the 'fancy one' is Win7/current games (I built it 3 yrs ago).
Now, I'm not going to say it's not more expensive than buying a console. It is. And consoles have PC's beat on ease of use, yup. If your income is very sparse, buying a cheaper non-gaming laptop for school/internet etc. plus a console is likely more affordable & flexible. But this whole myth that you're always replacing parts & that keeping up PC's to run games costs some kind of mini-fortune is a fallacy. Occasionally it may happen that multiple things break not far apart, but that's bad luck, which can happen to anyone (including console users), not the norm.
Edit: The current hard drive "crisis", however, may change things for that particular item. SSD's are still very pricey, relatively speaking, and depending on how things go with the rebuilding or whatever of that industry, quality of HDD's could be hit or miss more often for a while, plus price and availability.