Asus only boots into EUFI BIOS screen after win 10 upgrade.

This is more than likely a HDD issue if it has bad sectors. You need to get that hard disk replaced.

Was this also a preinstalled version of Windows 8.1? If so, you will need to install a clean version of Windows onto your system on a new hard disk

Do you have a Windows install disk? If so, insert the disk and go into the BIOS, and make sure your dvd ROM is set to boot first in the UEFI BIOS. When reinstalling Windows 10, make sure the UEFI only is selected in the BIOS.

If you don't have an install disk, you will need to get on another PC and download the Windows 10 media creation tool. This tool with download the installation media, and will give you the chance to either burn to DVD or save to an empty USB flash drive.

If you have already activated Windows 10, it will automatically reactivate after reinstallation.

UEFI stands for United Extensible Firmware Interface, which is a new way the system is able to interact with the hardware as well as the Operating System. UEFI offers the new secure boot feature made for Windows 8 and Windows 10. It also adds on a GUI interface for added mouse support, and has a lot more bells and whistles to ensure greater system performance, reliability, compatibility and stability. UEFI replaces the old traditional Legacy BIOS that was on older systems, However, it keeps compatibility for if you want to run a non UEFI system, such as Windows Vista or Windows 7. It's also for anyone who uses Linux.

Not always. You can go back to Windows 8.1 if you do it within 30 days. Now since its been 3 months, yeah it's time to do a clean install, or if you have Windows 8.1 recovery media, you can start there.

Although with a lot of the forums on here where people are expressing issues with Windows 10, that you should do a clean install. If you are wanting to keep your restore media, buy another hard drive, and the recovery is set.

If the Motherboard has a key like F11 to start the recovery of a recovery media, upgrading doesn't totally kill that. I've had to use the recovery media on a few systems and it has worked just fine.

When loading to a clean HDD, if you boot using the UEFI Boot loader, the Hard disk will be formatted in GPT.

The system will say, press any key to boot from CD/DVD if you install the OS from a DVD. Press any key to load from UEFI Boot Loader.

If you are using a USB flash drive, the system will automatically boot using the UEFI Boot loader.

If you type in your model name in Google, it will sometimes tell you which version of Windows came Factory with the board.

If you had Windows 8.1, you need Windows 10 Home.

If you had Windows 8.1 PRO, then you need Windows 10 PRO..

You can Download Windows 10 online by going to Google and looking for "Windows 10 Media Creation tool".

Keep in mind, the install media for Window 10 1511 has both Windows 10 Home and PRO versions on the same install media, so if you have that, you are good to go.

If you have Windows 10 PRO Version 10240 RTM, then you will need to use the media creation tool to download the new version

Also make sure to download the x64 bit media

It also says on the ASUS website that this computer with Windows 8/not PRO version.

Thank you maneke exactly what was required - I called Asus to check the version, and they confirmed it was "Pro". (MS stickers don't specify, perhaps Microsoft needs to re-think this one out, because when we have a dead hdd, how does one tell?)

I have installed win 10, and boots into 10 with a couple of caveats below), so we now know it wasn't a EUFI issue but simply a corrupted hdd. MS decision in regard to failing hdd's in 10 leaves much to be desired (can be checked in Events, but when the system is dead that's not possible).

The two issues I have may be due to the way I did the clean re-install. First I copied all partitions (including the System EFI ;partition) but not the damaged system partition. I did a clean install to this unallocated space (same size as previously).

Now when I boot I have two issues I would like to clear up:

(i) On clean boot it asks me which of two Win10 options I want to boot into. The new one is the default, the old one goes to an error. As there are 30 secs to choose, one could reduce this to 0 to resolve (how?); preferably to remove the options altogether?

(ii) it is asking me for a COA license, of course we don't have one as originally it was an upgrade from 8.1 where the licence is held within EUFI?

Any advice how to resolve these two issues would be appreiated - very steep learning curve with Win10!

When doing a clean install, you always must delete all partitions before doing a reinstall.
You never want to transfer partitions, unless you plan to transfer the os from one drive to another, which is using a system image to restore the OS. Reinstalling without deleting partitions will create 2 different entries in the BCD, thus causing you to have the dual boot configuration. If you haven't installed anything on the system, I suggest you boot into setup and do a clean install by deleting the boot partitions you transferred and start from scratch.

Windows should reactivate on its own if the hardware is the same.

Let me know, if after doing a clean install, if it still asks you to reactivate

Thanks I thought as much. Good to get confirmation. So back to the start! Will advise.