The PC does not have to be this big bulky and noisy thing. It's just been a trend that many gamers have these large maxi towers filled with huge fans and more lights then a Christmas tree..
I just built a new PC some weeks ago based on the mini-ITX motherboard form factor.
The PC case is 24x24cm and the height is 10cm (18cm including the modded GPU heatsink). It contains all the thing you need in your average gaming PC like a 3.2ghz (4ghz turbo) i7 CPU, 16GB XMP overclocked memory, SSD and a GTX750Ti gfx card.
And it's completely noise free and 100% passively cooled with no moving parts what so ever. And if you need a better GPU then the GTX750 Ti, just add a quiet 120x120 fan to the GPU heatsink. Use temperature control on the fan and it will still remain passive most of the time, and only spin when needed during games.