Thanks for your reply back. It appears that you have a custom-built or self-built rig correct? There are a whole slew of problems for WinX upgrades on self-built PC's; many of us Insider testers are focusing right now on the OEM or name brand computers (Dell, HP, Sony, Acer/Gateway, ASUS, etc.). Since your Motherboard has a modern processor *i5*, it sounds like it was built after 2010 or so and that's good news.
The bad news is that UEFI-BIOS based machines have multiple settings that preclude you from booting an external device such as a usb flash drive or external dvd-burner for examples. What I would do is try to figure out the BIOS settings on your Mobo (what brand is that; is it actually an Intel-branded Motherboard? Model number please!). Generally, you'll need to temporarily DISABLE your UEFI setting and change it to CSM mode. And additionally, you will need to set your LEGACY CSM sub-setting to ENABLE external boot, otherwise no usb or dvd can launch during PC bootup time. These settings have a variety of names, but mostly they look like what I wrote. If that fails, you may also have to go into the STORAGE section of your UEFI BIOS and change in SATA MODE from AHCI-->IDE MODE. This forces your disk controller chip on your Mobo to run in a slower speed SATA mode say 1.5Mbps instead of 3.0Mpbs/6.0Mbps, and allows backwards compatibility for OS installs. Took me years to find this out!!
So, if you still can't get your usb WinX to boot; you can do a simple test such as downloading a free utility such as MEMTEST or SEATOOLS (RAM & Hard drive diagnostics), install to your formatted usb stick and see if your PC will boot from either of these. If it can't, you probably have a series of settings in your Mobo UEFI-BIOS that are blocking external media boot. If that's not resolvable, you may have to replace that Mobo. You can also try calling Tech Support for your Mobo if available. If it's Intel, you can get phone support on your Mobo, but it may cost you $$. And be prepared to spend several hours on the phone to get this type of problem resolved. Worst case, if the Tech discovers your Mobo has a fault, they may just tell you to replace it; best case they may send you a new one for free!
Another alternative you have is to take your PC into your local Computer Pro or store (Best Buy Geek Squad or MicroCenter) and pay them to get the WinX upgrade done, and you don't have to worry about all this stuff!! <sorry!>.
It sounds like you might be a DIY guy, as am I, and you can attempt to figure it out yourself, but it's gonna be a challenge. Other forums I volunteer on covering WinX upgrade stuff, we have yet to address your particular issue. So, if any other Mods here have some other suggestions, I'm all ears; and am willing to learn some new tricks.
Keep us posted on your progress.
Best of Luck,