Pressing F8 as soon as you power up the computer will bring up the startup menu options on Microsoft products, but that is in a sense using the OS. Do you have a BIOS password that you are trying to crack? If that is the case, just do a search for BIOS password backdoor on the net. Most BIOS password on a Phoenix BIOS can probably be removed by simply disconneting the RTC battery (CMOS battey).