Skylake i7-6700K stress test crashes and overclock problems on Gigabyte GA-Z170-D3H board

[JBarn3]

New Skylake i7-6700K CPU installed in a new Gigabyte GA-Z170-D3H motherboard. I'm not able to change the clock speed and the computer crashes during stress tests. Not sure if it's a CPU or board problem so I'll start here.

The chip runs fine in this board, but I cannot access the base clock and multiplier settings in the BIOS. They are locked and show on AUTO, although with an unlocked chip like this the MANUAL option should become available but does not. The BIOS CPU UPGRADE option is available, which lists pre-set overclock values, +20%, +40%, etc. I've tried a few different BIOS revisions but no change.

Tried using Intel's Extreme Tuning Utility as well. Here the cores can be changed. But changed cores or not, when I run a stress test in this utility the computer locks or crashes only a minute into the test. Does the Prime 95 issue have anything to do with this?

My ultimate goal is actually to do some underclocking with this chip just as experimentation.

The board was previously used with another locked Skylake with no problems. OS is Server 2012 R2. I'm running onboard (chip) graphics only, no video card as this is a headless server usually controlled via RDC. Only other peripherals are a USB card in a PCIe slot and two SATA SSD drives. 16GB DDR4. Powered with a 160 watt picoPSU supplied by external 12 volt source.This is a heat-pipe-only server case, no fans, that so far has been very effective at heat dissipation, never a problem, the chip usually runs relatively cool.

[KTran10]

I think you are running into skylake bug relate to heavey workload, here is the link

http://arstechnica.com/gadgets/2016/01/intel-skylake-bug-causes-pcs-to-freeze-during-complex-workloads/ Intel Skylake bug causes PCs to freeze during complex workloads | Ars Technica

[Allan_J_Intel1]

I just received this from the engineering team: Intel has identified an issue that potentially affects the 6th Gen Intel® Core™ family of products. This issue only occurs under certain complex workload conditions, like those that may be encountered when running applications like Prime95. In those cases, the processor may hang or cause unpredictable system behavior. Intel has identified and released a fix and is working with external business partners to get the fix deployed through BIOS.

Allan.