I think I have noticed my SRock Q87WSA-DL Ami BIOS forgetting any USB boot instruction and booting from Hard Disk instead. I have to press F11 on boot instead. Even then, some live USB's have only booted when I select USB, not the newer UEFI.
For reference, I will say that I have found Qubes-R3.2-x86-64 is very usable when installed on a Sandisk extreme (USB3.0) 64GB memory stick. I created a boot USB on an 8GB Netac stick, booted on that. I then installed qubes on the larger and faster Sandisk, encrypting it with a passphrase. LibreOffice installed and ran fine. This was on an i5-4440 processor, with 4GB RAM, and AMD Radeon HD 6450 graphics card. Vt-d was switched on, communication was by Ethernet, and there was no TPM.