Why is this sometimes happening on boot?

[Jamarlie]

Maybe one of you tech savys can help me with my problem here:

I boot Windows 10 off of a regular 750 Evo SSD. 
Now sometimes when I go to start up my system instead of booting up Windows I just see a black screen and small blinking dash at the top right corner. Then nothing is happening. Usually that dash would wander down and Windows would boot up, dunno why it does that.
Shutting the computer off and back on usually fixes the issue.

I always thought "Hm, maybe my PC boots of any USB device for some reason and just gets confused, heck do I know" and went on my way. After all that only happens like 1/20 boots or so and has always sorta been there as a boot "issue" ever since I built my PC.
Today it happened three times in a row though, which understandably made me freak out a bit. I am now certain that doesn't originate from any other device as I went into the BIOS and specifically told my PC to boot the SSD, still the same problem.

It was only after shutting off the power and trying again that it booted just fine.
What the hell is this sorcery and how do I prevent it? Is it bad? Is it "just a Windows thing"?

In case you need specs or anything:
i7 4790K, GTX 1070, Sabertooth Mark S MoBo, 256GB 750 EVO SSD (I only use it for booting, it literally is about 2/3rds empty), 2 other Harddrives for everything else, Windows 10 Professional. Built the system in mid 2016 so I highly doubt something is extremely broken that causes this.
My SSD has 12TB of writecycles on it, and about 9500 hours of runtime. Crystaldisk says it's at 100% health.
Thanks in advance!

 

[Radium_Angel]

1 hour ago, Jamarlie said:

Thanks in advance!

Sounds like your boot drive is going bad...

Or possibly the sata port it's attached to, I've seen that too.

[Jamarlie]

7 hours ago, Radium_Angel said:

Sounds like your boot drive is going bad...

Or possibly the sata port it's attached to, I've seen that too.

But that would be weird. I've had that problem ever since I first built my PC. Needless to say that Crystaldisk doesn't show me any signs of trouble (although I do know that SMART doesn't necessarily mean anything):
 

[Radium_Angel]

Just now, Jamarlie said:

But that would be weird.

Yup, problems that don't occur all the time are difficult to track down. I have seen this before however. The drive doesn't have bad sectors, and won't trigger SMART, but nonetheless, there was just enough "oddity" to it, that it wouldn't boot properly.

 

Given how cheap SSDs are now, I"d grab a 120GB SSD, install a fresh copy of Windows, and see what happens. If the problem persists, then it's in the mobo.

If it goes away, it's the SSD

[Kilrah]

Motherboard might be going bad.

My old 2010 system works great - that is as long as I make sure I have nothing plugged in a USB3 port when I power it up (it has only 2...) or it will stay stuck on POST.

[Jamarlie]

Alright, thanks for your help.

[Jamarlie]

Okay, maybe a quick update, I seem to have found the problem.

I believe my SSD is fine, the issue has probably something to do with my keyboard. Now I was also able to reproduce how.

To "force" this error I can just hold down the power button on my PC which will make it turn off, turning it on again after that basically caused the weird pointer to flash again and not boot.
That's when I noticed my keyboard was faintly flashing when I did this, I presume it gets barely enough power from the USBs to vaguely kind of half turn on?
It's a Steelseries M800 meaning it's basically it's own computer. It usually requires two USBs to be connected for power delivery as well.

Now my theory was that the faint flicker of the keyboard probably draws just enough current to make my PC think there is a USB connected as a boot drive. Meaning my PC (most likely) effectively tried to boot from my keyboard, giving me this blinking thing. Disconnecting the keyboard and trying again resulted in everything booting up just fine. More testing might be required but I think I found the culprit.
I have absolutely no clue what causes this but if you happen to find this thread and have a similar problem: It was the keyboard in my case. That explains why turning off the power helps to not feed the CPU in the keyboard more electricity and therefore the PC booting up correctly.