Question Win10 will only boot via HDD to USB adaptor, not when plugged into motherboard

[crazybaresi]

Recently I've been experiencing lots of problems booting into Win10
First I had an issue that the PC would not boot first time, having to restart itself once or twice before finally booting after 5 mins. Frequently the system would get as far as the spinning dots under the blue windows icon and then fail.
Finally this week it stopped booting altogether and gave a stop code 0xc0000021a. I tried all the provided methods for fixing provided by Microsoft, including attempting reset, roll-back etc., but all failed for some reason or other.
I bought a USB 3.0 to HDD adaptor and tried to fix the Win10 installation via my laptop using various methods found on youtube e.g. chkdsk, scannow, dism cleanup etc.
Still no joy booting from USB.
But - I'm typing this now on the faulty PC because I managed to use the USB cable and boot from the 'faulty' windows installation via the cable.
So the question is: What is causing the boot failure if there is nothing wrong with the windows installation? Presumably RAM, graphics card, wifi, PSU, CPU etc. are all fine as I am using the PC now? I even checked the motherboard battery which reads 3.0 volts.
Any ideas? Otherwise I think I'll have to buy a new motherboard...
Thanks for your time


GA-X58A-OC motherboard
Sandisk Ultra II SSD hard disk
Corsair TX750 PSU
Corsair Vengeance 12Gb 4x3Gb 1600 MHz RAM
Coolermaster Silencio case
Graphics card TBC

 

[rgd1101]

try another sata port on the motherboard? try another sata data/power cable?

 

[crazybaresi]

try another sata port on the motherboard? try another sata data/power cable?

Thanks, I just swapped to SATA cable that was connected to my second hard drive (leaving the motherboard end of the cable in the port that was connected to the second drive and used the power connector that had been connected to my second hard drive. No joy.
Then I also tried bypassing the SATA hot-swap port and connecting the SATA cable direct to the HDD and a 3rd different power cable direct to the HDD. No joy.
In both these cases I end up back at the stop code screen...
Any other suggestions?