How to install and use Ubuntu from a USB flash drive on Windows 8? [duplicate]

Use the Universal USB Installer to copy your ubuntu ISO file to your USB drive and make it bootable, and on the step 4 you set the amount of space it will use to store the changes, this way it won't revert to the default state when you boot.

(This software is recommended on the official Ubuntu guide).

This is almost certainly a Secure Boot issue. The vast majority of Windows 8 computers ship with Secure Boot active, and it will prevent you from booting another OS unless that OS supports Secure Boot. Although Ubuntu 12.10 nominally supports Secure Boot, the statement that another computer was used to prepare the boot medium suggests that it was almost certainly installed without Secure Boot support -- and probably in BIOS mode, as well.

The easiest solution is to disable Secure Boot; however, be aware that the procedure to do this varies greatly from one computer to another. You need to dig into your firmware and locate a suitable option, which might or might not have an obvious label or obvious settings.

When you're done, you might need to try both of two boot options in the computer's built-in boot manager. One may enable you to boot the USB drive in BIOS mode and the other to boot in EFI mode. Again, the labels on these options can vary from one computer to another.