bro i can fix that, i have that same problem with my old dell p3 laptop
same scenario
no cd rom
usb booting does not support <of couse panahon pa nang mampor>
external cdrom doest not boot from the usb port, ky not supported sa bios
wala nako hilabti ang bios, ma corrupt pa lang nuon..
give me a txt or pm 0917-321-9057