|If something has corrupted your BIOS and the computer wont boot,then there is nothing you can do except obtain a new BIOS chip. You need to be able to boot the computer in order to update the BIOS.|
Are you sure the BIOS is corrupted? There are facilities built in to BIOS code in both hardware and software to prevent the BIOS from being written to while the OS is running. Stops viruses from writing to the BIOS which was very common at one time.
If your friend has found a way of circumventing these checks then I would not let him near your computer ever again. There is no legitimate reason to need to write to the BIOS while the computer is running.
Now if it is the CMOS memory that is corrupted, then that is a different matter. That can be reset to a default condition that will allow the computer to boot. You can do this usually by temporary moving a jumper on the motherboard. The motherboard manual will tell you how to do that. Or alternatively, remove the power cord and then remove the CMOS battery for a few seconds then replace it. The CMOS battery can be recognised as a silver disk about the size of a small coin.