Alienware desktop won't boot from USB

Hi !

I could use a little bit of help on this issue.

Long story short, I'm trying to boot from USB to install Windows on a replacement HD for an Alienware X51 R1. The BIOS POSTs properly then nothing happens.

The logical next step is to check the boot order but I can't because my USB keyboard only powers on after POST even when using the USB 2.0 slots. I reset the CMOS jumpers. I unplugged the CMOS battery and let it hang out for hours. No dice.

Any ideas?