No longer able to boot from USB
I have a 512MB Apacer Handy Steno USB pendrive, and it won't boot for love nor money. Yes, this model *is* bootable, it says so on the manufacturer's site, and besides, I've accidentally tried to boot from it before and got a "NO SYSTEM DISK" error (i.e. I had to unplug it in order to boot my PC from its hard disk).
I've not tried the HP format utility because I've heard bad things about it, but I've tried the PEtoUSB formatter and GRUB4DOS to install a boot sector. I've also tried the Debian method (i.e. zcat boot.img.gz > /dev/sdc). Neither works on my Asus A7N8X at home (which is the machine I've "accidentally" booted it on before), nor on my HP/Compaq PC at work (which actually lets me press F9 at boot and select "Boot from USB device"!).
I know there is a difference between USB drives which are formatted as hard disks (i.e. with MBR, partition table, etc.) and those which are formatted as "superfloppy" (all-in-one). AFAIK the difference is merely that you mount the former using /dev/sdc1 and the latter using /dev/sdc - and you have to tell your BIOS to use "USB hard disk emulation" in the former case. I cannot get mine to boot in either configuration.
Is there anything else I'm missing? Why would a USB stick which has been the boot device in my PC suddenly not want to do it anymore?
Is there a preferred boot loader for USB devices? GRUB? LILO? Syslinux? Something else?
Grateful for any help,