Welcome Steerpike.
You've already covered a lot of bases, a good start.
It sounds like there are no signs of error from the USB creation process, but apparently the USB is not identified as bootable.
Not sure about the age of your Satellite, but I assume it has booted from one of the previously-successful USB sticks. So boot from USB is possible.
Were any of those successful boots using Ubuntu-based distros ? (microwatt R9 is based on Ubuntu 14.04)
When the Satellite boots, can you read the USB stick which it has ignored for booting ? Or is it ignored completely ?
Does your Satellite have a UEFI mobo ?
You're obviously aware that there are non-apparent differences among USB sticks. (In my case, I used a Strontium stick for data, and still do, but it flatly refuses to behave as bootable, just as you're finding.) Sadly, we seem destined to discover this the hard way.
A couple of possibilities for you :
- you might need to format the USB stick back to FAT32 before you start (can elementary or Win10 do that ?)
- using Rufus under Win7 works smoothly, and I assume also under Win10 If you read instructions online, make sure they're for a current/near-current version of Rufus.
- if you search online, include Ubuntu 14.04 in the search .... too many of the fail stories are now out-of-date
When you solve this, there is an audience who'd love to know !
Best of luck