Missing Operating System!

"Missing operating system." This was a problem bugging me for the past two days. Background: I bought a USB flash disk to use to install Ubuntu on CD-ROM drive-less computers. It worked well enough the first time around, but after I reformatted it, I couldn't use it to boot the PCs anymore. The recurring message: "Missing operating system."

I searched the forums and sites high and low, but couldn't turn up a satisfactory solution to this problem. Tried reformatting several times -- with gparted, with mkfs, with fdisk -- all to no avail. Tried reinstalling with usb-creator. Tried various ISOs.

Ultimately, what did the trick was to delete the partition using fdisk. Apparently, the partitions on the USB flash disk weren't properly set. I don't know how it happened. Deleting all the partition on the flash disk with fdisk did the trick.

Then, next step was to recreate the partition on the USB flash disk, but this time using gparted to do it.

A subsequent check using fdisk showed that the partitioning problem had gone away.

Finally, usb-creator one more time, and it all worked.