HP Laptop stuck in reboot cycle (won't clear POST) after BIOS upgrade

Fixed it in the end using wincrisis.

If you can find a copy (apparently versions prior to 10.0.0.4 do not support USB drives), then download the BIOS from HP, run it and note the folder you save the files to.

Ignore the warning about the flash failing on an unsupported system and go to the folder the files were saved in. In there there should be one or two files with a WPH extension.

Copy either of these to the folder wincrisis.exe is in, and rename it to BIOS.WPH (may be case sensitive) then run wincrisis.exe and let it format the drive and copy relevant files.

Then plug this into the laptop and hold Windows+b and turn it on. When you see the USB drive activity LED start blinking you can let go off the keyboard. The LED should solidly blink away for a few minutes. Then it stopped and the fans started running loudly for a few minutes, then it powered itself off.

If it doesn't work, try another USB drive. Apparently 512Mb is optimal but I used a 4Gb. Also wincrisis.exe doesn't seem to work on my 7x64 pc but ran fine on an XPx86 box.

Turned it on and job done.

HP says to unplug everything. What does "everything" mean to you? To me, it means the battery, hard drive, optical drive, mini pci cards, any USB devices... even Ram the first time. Why? Without Ram it should produce a no-ram POST beep error code. If you get that, then insert one stick of Ram and try again.

The point here is to remove everything possible to eliminate and isolate the components from the issue. Due to the age of the unit, it could be coincidence that the problem happened after the BIOS update. No way of knowing until you are reduced to a working display, a motherboard with processor, working Ram, and power.