You don't say which version of the MSI MS-6590 you're using (there are three), but taking a quick look at one of the manuals, I don't think you can boot from a USB stick.
The best thing to do is go into the BIOS and check if booting from USB is an option.
Having said that, you're suggesting your manual says it can, which is a puzzle.
I will say this however. If you're using a seven year old motherboard, at best, it would be flaky as to whether USB would boot. That was about the time the option was first introduced and was notoriously unreliable.
The situation has improved more recently.