Hehe… I’m all too familliar with that mindstate!
Right. Intresting. I think on the LED page they are talking about the main LED, it is solid red when the pixhawk is in error, not the FMU PWR or those other small ones. The pixhawk 2.4.x is open source hardware, so different manufacturers will put different colour LEDs (pretty sure those small LEDs are single colour) and you just happened to have got one with red LEDs (congrats, they may be very rare )
Hmm… so this means there is some sort of AP code running on the pixhawk (if the chirpy noises and main LED works)… Looks like the damaged bootloader isn’t allowing you to update it.
No problem, a quick tutorial it is!
So, stm32 MCUs all come with the factory bootloader on them, which cannot be erased, and this what they mean by DFU mode. The way you access it is by giving +3.3v (NOT 5V!!, it could damage the MCU) to the boot0 pin and 0v to the boot1 pin (which, on the pixhawk, is already grounded so no need to worry about that) on the MCU and then powering it on, and it should land in DFU mode.
Now usually most pixhawks come with a pad that goes directly to the boot0 pin on the MCU, and DFU can be accessed by soldering a jumper from it to a +3.3v pin on the board and then powering on, but the issue here is most. One of my pixhawks didnt have it (atleast not at the specified location). Could you post a detailed picture of both sides of your pixhawk board (open up the case and send the internal board) so I can try and point out this elusive pad?
IMPORTANT - There may be 2 boot0 pads of your pixhawk, one is for the IO processor, and the other is for the main FMU, the latter is the one we need.
Are you okay with the software bit? If you need any help with that, just ask! Lets get back to it once we’ve identified the boot0 pad.
Also, read this: How to enter DFM mode on Pixhawk
 One more thing: your sure its not a pixhawk to PC communications issue that preventing the firmware update? Usually bootloaders don’t just go ‘missing’… Maybe something happened, I’m not sure. Can you connect over mavlink? (assuming some AP code is running on the PH). Lets keep trying the DFU as well, you never know.