If it hangs at POST it probably indicates a defect with a critical component (ie. not a component like the hard drive, but a component like the memory/mainboard/CPU). It sounds like you've done everything you can to try and alleviate simple issues with CMOS corruption/bad seating, so I would suggest there is an actual defect on the mainboard or a problem with device enumeration, there nothing to speculate any further than that.
baka yung HDD nyo na ang sira.