Trying to boot computer from USB stick but I can't get either F-12 (boot menu) or DEL (BIOS setup) to work. It looks like it flashes on for about 500ms, then goes away and moves on to normal booting from my hard drive. I know that the keys both work in normal booted up mode so I doon't think it's a keyboard problem. Have i somehow locked myself out of BIOS? I haven't flashed it or anything weird like that. Any help appreciated.