Yesterday, I wrote about not having to wait for Windows 10 to be advertised to my PCs and downloading the software directly instead. Unfortunately, things didn’t turn out to be quite that simple.

Overnight, both the Windows 8.1 PCs in our house decided that Windows 10 was ready (I clearly need to be more patient) but my 10 year-old son wanted to perform the upgrade (he’s a trainee geek) so, I waited for him to come home tonight before we tried it out. Because I’d already downloaded the media I thought I could skip bringing almost 3GB down over my ADSL line and boot from USB but we had a little trouble along the way…

I’d prepared a USB flash drive from the Windows 10 .ISO file using Rufus but our family PC (a Lenovo IdeaPad Flex 15) didn’t want to boot from it.

First of all, I had to work out the boot menu key combination (F12) but, even then, the boot menu only wanted to boot from the network, or from the local hard drive. I checked the BIOS (F1 at boot) and USB boot was enabled. Following Lenovo support article HT076906 (How to enter Setup Utility (F1) or Boot Menu (F12) on a Microsoft Windows 8/8.1 preloaded PC), I tried various combinations to reboot the machine (including Shift+Shutdown for a full shutdown and Shift+Restart for Windows boot options) but nothing was helping to boot from USB.

I tried recreating my media using different partition schemes for UEFI but that didn’t work either. So I followed Lenovo support article HT078684 (Cannot Boot From a USB Key – Idea Notebooks/Desktops) to:

1. Run cmd.exe with Administrator privileges.
2. Insert the target USB boot media device into an available USB port.
3. Type:
   diskpart
list disk (and make note of the disk number of the target USB drive)
   select disk n (where n is the target USB drive noted earlier)
   clean
create partition primary
format fs=fat32 quick
active
assign
list volume
exit
4. Copy the entire contents of the Windows ISO onto the newly created UEFI boot media.

After this, I successfully restarted the PC, using F12 to access the boot menu and could boot from USB (i.e. the flash drive was available in the menu).

Unfortunately, after all that effort, Windows 10 wanted a product key to install (which I didn’t think I had on a PC that came with Windows pre-installed), so I went back to an in-place upgrade using Windows Update.

It’s been a few years since I regularly built PCs and it seems my desktop skills are a little rusty… since then, I’ve discovered a number of utilities for reading the product key of my Windows installation (which is also stored in the BIOS) – the tool I used is Windows Product Key Finder, available for download from CodePlex.