UPDATE: I've flashed the latest BIOS, and was finally able to boot into Windows. Then I started a Windows refresh, and then the system rebooted, I'm back to the same USB error... At least I was able to turn off CPU fan monitoring after flashing the latest BIOS, while everything worked well, so the CPU fan error is gone. After the first reboot following the successful flash and booting into Windows, I'm back to square one, more or less.

 

Unplugged the front panel USB headers?
Checked the physical USB ports for damage?
Check for oxidisation on the board?

Set it up on a non-conductive surface, i.e. mobo box and see if you still have the same issue as it could be a case short.
Otherwise probable that something has just died

 

Yes to the three questions--all good.

Yeah I guess I might need to test it outside the case (which is a pain, because it's a large motherboard, and the CPU cooler is big too).

So far, I can boot completely normally if I reflash the BIOS. I've just done a second BIOS flash, and now again everything works okay. I suspect until the next reboot.

 

Tried booting outside the case, same deal I guess something is wrong with the motherboard.

 

What were you doing right before this error showed up?

 

This is most likely due to one of the PTC SMD fuses being triggered, some times they don't reset properly. You can check if they have 5V on both terminals, if it only has 5V on one side and much lower on the other you've found the issue. They are located close to the USB ports, both external and internal. Example of what they look like attached. Usually they can be fixed by simply heating them to ~70*C with a hair dryer.

 

Very interesting. I've looked for those, and on my board model, there's one at the front of the motherboard by the rear I/O panel and one on the back on the opposite side. I've reflowed both sets of joints. I don't know if it helped, but I no longer get the USB error! THANK YOU!! <3

However something else concerning is happening. The motherboard flex is causing the board to either be stuck in boot message 00 and not boot past that or boot normally if I flex the board a bit. Hopefully once I mount everything back into the case, the tension/shape of the motherboard will be correct for boot. I guess it's getting old and some solder joints are not great now that this is happening?

 

Well so far so good... Everything back in the case, all components connected, working through Windows refresh and crossing fingers. Has rebooted without issues a few times now on its own.

I'm using an MSI GPU bolster support to also prop up the heavy CPU cooler (Be Quiet! Dark Rock Pro 4), to help avoid motherboard flex. It's great, I highly recommend it.

 

Glad to see you have it sorted out! I have the same cooler but with the optional third SW3 fan attached (Three fans) and i agree absolutely a great cooler.

 

Your just saved my pc, thank a lot man!