I got a GTX970 yesterday and everything worked fine at all, installed Windows and everything, but after a random Windows reboot I initiated myself, the screen suddenly stuck at black, PC also seemed frozen (numlock wouldn't toggle if pressed). Reset/powered off PC a few times and it showed all different scenarios, like boot loop (on fpr 10 seconds off, on again), or just went on but frozen everytime no picture. I tried everything from plugging HDMI into on-board, DVI nothing. Then I reset bios via button on the back and picture came... I went into bios, just deactivated a few things like comport and Intel Rapid start, activated HDD Smart, nothing special, no overclock settings! Went to save bios and exit, and then the picture froze for about 5-10 seconds (never happened before), and pc went off, and automatically on again, and again black screen...

I checked if bios battery is still fine, it was.

I did a bios reset again and then it worked again, I went into bios again disabled those unwanted things, saved, and this time it worked, and I could boot Windows. I downloaded a GPU stress benchmark to check if power supply maybe could be defect, but it went on for about 30 minutes at 99% GPU load, no freeze or BSOD.

I googled about this and there are lots of posts about "GTX970 black screen" issues, mostly a lot of different problems, but some posts there was a need of a bios update for some Asus mainbords, some people suggested to deactivate "Intel Dynamic Power Technology" in bios, which I looked for but couldnt find it, dont even know what it does.

I also thought it could maybe be related to UEFI boot/CSM turned off/secure boot, because right now I have it to CSM mode (no fast boot), and it workes again "so far". But the funny thing is, I never changed anything in the bios for the last years, it always worked fine with fast boot (CSM off), and also I would assume GTX970 is fully fast boot compatible. So could it maybe be a bios bug?

Could it be that Extreme 6 Z77 has some kind of incompatibility with GTX900 series, and would need a bios update? I have the newest bios of course but it is from late 2013 (ver 2.80) I think.

Hope someone can help me with with.