My solution (tested on Gigabyte GA-P965-s3, Award bios, Windows 10 installation):
- from Windows format your USB stick to FAT32 (default allocation size)
- paste your Windows 10 image in UltraISO, choose "USB-HDD+" as writing method
Notice: I got Windows 10 image via Media Creation Tool wherein I chose exactly single bit edition (x64 in my case) instead of "both x64/x86 edition", thereby created ISO weighs less than 4gb so it doesn't create any problems for old motherboards
- after successful writing plug your USB stick into the rear usb port of your motherboard instead of usb port on front panel
- enter BIOS settings -> Advanced BIOS settings -> Hard disk boot priority, move USB-HDD to the top of the list, save changes
- exit bios, press F12 to enter list of boot sources, select "USB-HDD"
- after installation your PC will reboot automatically, after then go to bios settings -> Hard disk boot priority, move your normal HDD to the top of list, save changes and exit bios, installation will be automatically continued from your normal HDD