I am a totally newbie in Linux world, I like to install the distro on my USB stick to see if the distro suits my needs
without worrying about conflicts with Windows on my HDD. What I can say is that I tried unetbootin only two times.
Only one time I managed to make the distro working by installing it this way. In my opinion, there might one problem
occured, something has damaged your boot loader so it wont work - only amateur guess, but what I know for sure is
that many distros have their own installation process right on LiveDVD/CD, so you can run the LiveDVD or CD and
install the system on your USB stick right from there. Untill now I've installed about 4-5 distros and they worked very
well, nothing happend with the boot loader on the USB stick. Try that, too. In my opinion it's the same - you can lose
nothing. The only difference is that this way you actually install the distro on the USB stick and the other way, there
is only LiveDVD/CD files transferred from DVD/CD to USB, so you can boot from USB, but it's not actually installed.