That was the first corrective action I took.
Started up with two different HDDs in or out of the console. The blinking red light will occur before the HDD even has a chance to access, meaning terminal hardware failure.
You can hear the PSU click off immediately before the red blinking lights start (may indicate a blown PSU).
Yellow light actually means HDD failure, and it should show up where the HDD access light is near the USB ports rather than the power up LEDs.