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I'm getting an i7 6700k with a Z170 motherboard. Is the Z170-AR good enough? Or should I go for a different company/specific board? Like what is the actual difference between them - eg the ASRock Extreme7+ which is about $100 more expensive.
The differences between various boards essentially come down to features, looks, and reliability. If the features of the Z170-AR suit you, and you're happy with the layout in terms of available slots, ports, and so forth, there's no reason to spend more in my opinion, and Asus boards tend to be pretty solid in terms of reliability. I don't have a "go-to" recommendation for Z170 boards myself but someone else may chime in.
Also, I have THIS SSD http://www.samsung.com/us/computer/memory-storage/MZ-N5E250BW which from what I have been told is meant for a laptop. Is there any way for it to work in my desktop?
All you need is a board with an M.2 slot, and it'll fit right in and work in a desktop board. The Z170-AR has one of these slots, most boards these days do have one or two anyway.
Finally, my computer is making a lot of noise... Is this because it just hasn't been cleaned in a while, or is there something I can buy / etc in order to quiet it down a bit?
That depends what's making the noise - I realise that sounds like an obvious thing to say, so let me explain. If it's fan noise, then it probably does just need a good clean. Even a small coating of dust on fan blades will make the fan louder for two reasons, one because it becomes less aerodynamic so it doesn't cut through the air as cleanly, and two because it will push less air due to this so if it's a variable speed fan, it'll most likely need to run faster to push the same amount of air as if it was clean. Also, dust can greatly reduce the efficiency of heatsinks, again a small coating of dust will reduce its heat transfer capabilities meaning the fan will have to spin faster to cool the CPU/GPU/whatever it's cooling.
So, if it's just general noise, then yes, cleaning your PC inside will more than likely quieten it down. Spray the inside with some compressed air to dislodge any loose dust, carefully wipe the fan blades with a soft cloth or some kitchen towel, and the same for the heatsink if it's easily accessible, you could also use cotton buds/q-tips (depending where you're from/what you call them) for this. Don't use a vacuum cleaner! This will easily kill components due to static.
If you have more of a grinding or clicking noise, that could be a HDD on the way out, or a fan bearing failing.
If your machine's still loud after cleaning and it's not a failing fan or HDD, there are a few other options (dried out thermal paste springs to mind, depending what sort of machine you have, some OEMs use paste that tends to dry out after a few years and therefore the heatsink doesn't cool the CPU effectively meaning the fan gets rather loud).
Regarding your build, if you'd like to post a complete list of any parts you're reusing and what you're thinking of buying, I'm sure we can offer some advice and guidance on any changes that might be of use - you may be able to save a little money here and there, or get better bang for your buck.
