My PC's dead... need help finding the faulty part

but hell I've never seen a Intel CPU die

I have. Many, many of them, especially back when I would LN2 overclock.

Pull it and check the wafer. Those CPUs are notorious for bending and causing problems under the pressure of some CPU coolers. The wafers are much thinner than previous gen CPUs. It could still be the mobo, so check the socket and make sure there are no bent pins.

Read

Does anything show up in windows event log?

Boot Linux from an USB stick and see how it behaves? Maybe run a CPU stress test like Prime?

Any beeping sound after you turn it on?

Try the linux on usb with only the mobo

I too have an Asus Z170-K - I have had several boot issue events with this motherboard since I got it, Have you updated the bios?
There up to Bios 0601 - but Ive been pretty much fine since Bios 0506.
Drove me mad at one point with a very similiar issue is all
http://www.asus.com/uk/Motherboards/Z170-K/HelpDesk_Download/

Whats the PSU wattage?

when you see the bluescreen, can you see any driver (.sys file)? that might help to find the problem.

In case you don't know Trinity rescue kit, you may want to have a look to it: http://trinityhome.org/Home/index.php?content=TRINITY_RESCUE_KIT____CPR_FOR_YOUR_COMPUTER&front_id=12&lang=en&locale=en
Basically, it's a light linux that can be used on USB stick. It comes with a lot of tools, you may be able to gather informations by manually checking windows logs.
I also found this tool: https://downloadcenter.intel.com/download/19792/Intel-Processor-Diagnostic-Tool I never used it, but it may help you diagnose a potential CPU failure. According to the page, there's a linux version.

Have you tried following the advice for Win7 from this post? The motherboard requires slipstreamed USB3 drivers which Win7 install does not include natively. https://downloadcenter.intel.com/download/25476/Windows-7-USB-3-0-Creator-Utility

https://www.reddit.com/r/buildapc/comments/3h8vk0/build_help_installing_windows_7_on_skylake_z170/

Do you have one ram stick or two? I know you used mem-test on it, but maybe try each stick separately, and in different channels to completely rule the ram out.

Something bugged me after I read your thread, but now it finally came to me: remove the RAM and use only one stick. Check again with all sticks, single stick only at a time. If it works and boots, then I hope that mobo is still under guarantee because it is an issue that may happen with Z170 ones.

Try to buy a cheap LGA 1151 cpu to test (celeron) or try find with friends.

Check your Ram, MemTest86 google it, blue screens , are 90% of the time connected with Ram.
My cousin had brand new pc with broken ram, so it happens.

I would check the ram and hard drive first regardless if you think there both working correctly. I've seen faulty ones do weird things. Also are you sure no malware got onto your computer it could be causing the error as well.

The harddrive could'nt be the culprit since it doesn't boot the usb key to install Windows... it blue screen too

have you tried to just simply pull the hard drive temporarily and seeing if the windows (or linux) bootdrives start fully up?? it could be as simple as the hard drives controller board is wonky and going out slowly and causing windows &/or linux to crash even though they are running off the pendrives.. operating systems still check other hardware and initialize them to use.

Check your BIOS settings and BIOS version, you might need a newer version of your BIOS to use some of your parts. I solved the exact same problem by resetting my BIOS with jumpers.

This is probably RAM / RAM slot issue.

I had a bluescreen problem with client's company laptop this morning. i3 running on 4 GB (2x2GB) sticks. I removed one and it's running fine now.

Guys... i think I can now safely say it's the processor. With the information gathered from the sysrq key I've looked in the manual and found a way to disable SMP (which is what seems to be the problem in the sysrq). In the bios i've forced only 1 processor and the system now boots. I've installed Intel CPU tester and it fails... Something about the frequency... I then proceeded to raise it to two cpus and it did boot without problem... same error on intel tester. Then tried with 3 and it hangs on boot. Then I returned to two cpu and activated Hyper threading... and it booted. Looks like processor 3 is dead... 4rth might be dead too.

Here's a photo of the intel tester with error :

http://s12.postimg.org/iijeirm0p/P1040638.jpg

Humm try with other ram or 1 module each time, give a clear cmos and just to be sure unplug all but the mb+mem+proc+hd(would be good to try instal on a pendrive too to see is the hd is not the source), also try it outside the case, i have see a lot o weird errors on my life that happened over some strange effect that cases make.

What other peripherals do you have in there? DVD drive?

I've put together 30+ computers over the years, and switched roughly the same amount of CPUs, and not once have I seen one go bad. Hard drives (with a clear lead), PSUs, graphics cards, memory, mobos, all fail, but never one single CPU, AMD or Intel. It seems Intel is really lowering the bar with Skylake.

Well, mind BIOS config, maybe it can be the source of your problem, clear the BIOS, low the RAM frequency and try a linux live CD to boot.
Skylake is making history because it`s easy to bend.

Well guys, the remplacement CPU arrived today. Reinstalled everything in the case and it works. It finally really was the CPU. Intel Customer support is... weird but I did get a remplacement which is all that matthers. Thanks to everyone.