I looked up the specs on your machine and with a 500 MHz Celeron and
max. of 192 MB of RAM it must be somewhere around 9 years old. I think
the problem is at least partly in the BIOS and partly in the chipset,
which probably doesn't even have an upgrade available now. In other
words, if you don't have BIOS support for booting from flash or
external CD/DVD Drive it doesn't matter what keystrokes you hit it
just won't work.