Well this thread gives me hope.
I just got a new (to me) N54L and I can't get it to boot from the USB. I have a N40L too and it runs perfectly.
The N50L will boot stuff like a freeDOS BIOS update (TheBay) just not the boot loader. Drives me mad.
Could it be that it doesn't like the USB stick? It's a 16GB USB3 Kingston Datatraveler. Should I try to find an older USB2 stick?