|OK, I have a solution.|
In my case it was a G62-228 CA laptop, that failed to boot after a BIOS update.
When I powered up, the fan would come on for a few seconds, the screen would display the HP logo, and show " Press ESC to enter BIOS setup " and then shutdown, no matter what key I pressed (ESC, F8 , F10). I called HP service and of course it was out of warranty, and after no luck over the phone, they suggested that I return it for repair for $380.
After several hours of internet searching, I found that pressing Win+B gets it to boot from a CD or a USB key, and restore the BIOS. When I pressed Win+B and then powered up, the laptop stayed on, and said "recovering BIOS" and then "Writing BIOS" and "Verifying BIOS" After this it shutdown again, BUT the next power up it came on for longer and said "BIOS recovered successfully" and SOMETIMES (about 1 in 4 times or so) booted into Windows. The SOLUTION is, after getting it into Windows somehow (through this tortuous process of recovering the BIOS, which I think reloads the corrupted BIOS and doesn't fix the problem) you have to run the sp52598.exe file which you can download from the HP website. This file is an executable, which loads the "Insyde" utility and allows you to load the new BIOS. After I had done this, the laptop worked fine.