Generally it is not a good idea flashing the bios from within the Windows environment. These are recommended DOS flashing methods in this order, USB stick, floppy, or CD (beta). Check and double check that you are downloading the right bios ROM from the website. Open your user manual and see: Updating the BIOS with the Q-Flash Utility
Before flashing the bios restore "setup defaults"
After flashing the bios and it has rebooted, go back into the bios and do this:
Shutdown by PSU power switch. Unplug the PSU and remove CMOS battery and discharge the motherboard by holding in the power button (not PSU switch) while touching the metal part of the case for approx 30 sec. Put the battery back in and post. Don't forget to re-apply your bios settings.
One last thing, not all USB sticks are bootable. You will know because your ROM will note be detected by your bios update utility. If this is the case, do this:
Make USB stick bootable (only if hidden MSDOS files are not present on USB stick) with the HP USB Disk Storage Format Tool, you will also need MS_DOS System Files, you can download both here:
http://www.filefactory.com/file/ag [...] _v2_18_zip
Format to FAT or FAT32