Sleep causing unresponsiveness.

could be the same problem as mine reported here

I have the same problem. I have an Z170 Extreme7+ and an XFX HD7950 3Gb. I mention the video card because it's a hand-me-down from my previous build (have to do what I can to keep the cost down) and it did the same thing there. By "the same thing" I mean that upon hitting a key to resume from sleep the fans would start spinning and everything looked like it was going to come up, but the monitor never woke up. Holding down the power switch to power down completely and then powering back up successfully resumes windows after the post screen every time. The video card is especially suspect because in the old build, the trouble began when it replaced a 5870 which was able to resume from sleep just fine.

I now get the exact same behaviour in my new skylake build. The old system was an ASUS X58 with a first generation i7. The new build uses the same video card, keyboard (ideazon) and DVD drive, the rest is all new, even the mouse.

I, too, had a debug code of 55 when this happens. Memtest shows the memory is just fine. Updating the UEFI from the 1.8 the board shipped with to the current 2.6 gave no change in behavior, but now I have the side back on the case and the unit down beside the desk, so I have not verified that the debug code has not changed. Changing the UEFI setting to use the XMP (instead of SPD) for the RAM also made no difference. I did not try moving RAM around, nor doing all this with only one stick installed. I have not tried using the onboard graphics to see if the problem persists. Nor have I bothered trying a different keyboard or tried using the PS2 port instead of USB. All of those things are probably worth trying.

As if I haven't rambled enough, I have my RAM in A1/B1 (not A2/B2 as the manual suggests) because the first board (I am on my second extreme7+) wouldn't post (error code 5d) with the RAM in A2/B2. So when I got the new board I assumed the same thing would happen and started out with the RAM in A1/B1.

Hopefully you can identify something our builds have in common which may help you.

Good to know, thanks.

Also I should have mentioned that I'm using corsair DDR4 3000 memory.

I would recommend using the support page and sending a support request on the matter. Tech support does browse the forums from time to time but for more pressing issues it is always best to try Support directly. If you do not get a response in a few days send another request (excluding weekends). It can take a while for tech support to get around to you and sometimes requests may be missed but keep trying, Tech Support has always been very helpful when I have contacted them myself. Bare in mind that they handle hundreds of requests almost daily