There are many users suffering the same symptoms, it is a long read but find a thread over here.
Basically we find that disabling CStates completely seems to remove most of the crashing but does not fix 100%. Many have tired memory timings, changing boards, RAM, power, but the crashing remains.
Some find it happens every 5 days or so, usually idle, some find it happens all the time randomly. Always a hard lock, mostly when IDLE (screen blank) or just into IDLE from load. Some find with large amounts of IO (like partition move or 40GB copy disk to disk). Most with this problem find CStates on impossible (crashes within 10 minutes of boot).
I changed my CPU and the new one is much better, I can have Cstates ON, however it does hard-lock sometimes still.
I would like to recommend you to download and run the Intel® Processor Diagnostic Tool
Also, run some bench-marking tests with third party software to make your processor handle some good workload and see the behavior of it.
I was reading the thread mentioned before and some troubleshooting noted there could also be tested in your system.
I look forward to your reply and outcome on this.
OK, I have some feedback.
The Intel Diagnositic tool passes on their systems and mine. With Cstates ON on their systems it still gets through (the crashes happen when IDLE mostly) but the systems are not stable with CStates ON. Memtest86 passes in all cases (with a few deviants but you cant be sure they are not just statistical noise).
I am corresponding with another user here and this is also some feedback I gave him.
Everyone suffering the CState freezing seems to have Microcode 39. They all have the latest BIOS from the respective vendors, most with Beta BIOSes. My old CPU i7 6700K had the same problems which is why I am involved with the others, and changing only my CPU to another identical i7 6700K fixed them for me, I have Cstates ON with reasonable stability now. However my CPU is at Microcode 55. Since I tested the old CPU and the new one with zero other changes, same BIOS, same MB etc etc, and since the old one hard locked all the time with CStates ON and the new one doesnt, I am left confused from my side. I do have hard locks under transcode load randomly (more then the load in the intel diagnostic tool) but my hope is that these locks are the other known issue with Skylake and I dont want to confuse the two issues here. If microcode comes from the BIOS, why would the OLD CPU be suffering CState locks and this one not, if a microcode issue? Strange I think, but equally strange that they all have 39 and I now dont.
Lots of people report that changing RAM makes things more stable, some say increasing vCore to 1.2. But in all cases they leave Cstates OFF still; so I honestly think that these things a individual and not enough evidence exists to say this is a cure or just a lucky hit.
Is there a way to deliver new microcode (in OS driver form) so that they can test it?
Thank you very much for your time and feedback. A lot of very fed up people monitor on that thread and I would not like to guess how many are there in the background reading each day.
Let's continue with the original thread for this situation.Skylake hard locks seeminly when IDLE / CStates ON
This is to keep everyone on the same page regarding workarounds or possible future fixes for this.