After an HVAC crew at a customer's DR site triggered multiple power outages, their recently repurposed ESX host (an HP ProLiant DL360 G9), which wasn't connected to a UPS at the time, would no longer pass POST. It would stop at 'Loading System Firmware Modules' before faulting and hitting the RSoD. After trying multiple options we thought the power surges/outages might've caused a hardware failure, but the errors from the RSoD didn't seem to indicate this to be the case.
I found a related article (https://support.hpe.com/hpsc/doc/public/display?docId=mmr_kc-0128466) that is geared toward issues relating to BL460c's not being able to POST after firmware upgrades, and decided it was worth a shot before going down the hardware replacement route.
"SYMPTOM: Server May on Rare Occasions Stop Responding during Power-On Self-Test (POST)
This issue occurs because the server reads unexpected data values from the Non-Volatile RAM (NVRAM) or has found a boot block corruption and may exhibit one of the following symptoms:
• Server may not display video
• Server NIC port may be disabled
• Server may not boot
Cause
Non-volatile ram (NVRAM) holds its state after the master device/circuit is powered off. Hardware typically use CMOS (complementary metal oxide semiconductor) to implement NVRAM and incorporate a battery power source to retain system settings. That clears the current assignments of IRQs and such. Unless user have a hardware conflict.
On the system board, there exists a 'System Maintenance Switch' with multiple pins for performing different actions. We had to power down the server, then switch pin 6 (Clear CMOS and NVRAM) to the ON position, power up the server to clear NVRAM, power it back down and change the pin position back to off, and finally power it back up. Thankfully, this cleared up the issue completely and the server could boot up without problem. Just keep in mind all your potential alternatives before assuming a hardware failure.