Someone please help me! I am new to Linux.... I have been trying for well over 24 hours to get a ISO that will work on my Lenovo G500s, other that Ubuntu. I really wanted to use Cent OS 6.5 but can not find a ISO that will let me set up on USB to dual boot. I am getting a little stressed out. I have unbootin already, 128GB 3.0 PNY USB fresh with nothing on it, I can get in and out of my boot setup, system is backed up. I just can not get a good ISO that will show up in boot menu setup. I have already booted from USB with Ubuntu, however I can not find or get a ISO for Cent O.S 6.5, Red Hat, or Mint. I am not one for quitting, so I will be here a long time or until someone is kind enough to help me out.
Lenovo G500s
ic.5 with Windows 8.1
500Gb Samsung SSD Main
1 TB Samsung SSD 2nd int. drive

It isn't really clear what you are trying to do. From your post, I understand that you have one operating system on the computer, windows 8.1. You mention that you booted Ubuntu from a usb. Did you use unetbootin to put Ubuntu there? What boot menu are you referring to? Do you just want to create another bootable flash drive or do you want another operating system like Mint on the flash with Ubuntu. Either is doable the methods are different. I expect it is something like this as I can't imagine you can't find an iso for any of those distributions.

I am sorry. I am trying to get the proper ISO, so that I can download either Cent os 6.5, Mint, or Red Hat to dual boot from, using a USB. I was able to use Ubuntu, so I no that I do not have some settings off in my boot menu. I have tried mutable iso's and can not seem to get either one that will work, or I am doing something wrong. I can not get some other form of Linux to work for me.
Yes I am sure that I'm messing something up! I do have Unetbootin, and I have tries to reformat and mount several other operating systems, which that is exactly what I am trying to do. Get another op system from linux that I can work on
Thanks for getting back to me,

https://www.centos.org/forums/viewtopic.php?t=26420

Well from 2010 so CentOS seems to be OK to install on a G500.

http://wiki.centos.org/Download

Same as CentOS 6.5 (PS, I don't run rpm based distros)

https://www.scientificlinux.org/download

You might want to wait on Mint till the end of May when they catch up to Ubuntu 14.04.

I did a core install myself of Ubuntu 14.04 to avoid Unity,LDE,and XFCE and just run Icewm inside of Ubuntu 14.04 for myself.

It still isn't clear to me. Are you trying to dual-boot two systems off a usb or flash drive? Are you using unetbootin to try to do it?

If you are just trying to install another of the systems you mention, it would be the same process you used to put Ubuntu on the usb.

the normal CentOS 6.5 install dvd will install onto a thumb drive just fine
burn the iso onto a dvd ( as a IMAGE)
plug in the usb and pop in the dvd
and reboot
install to the usb

QED

BUT CentOS is not the best choice for running off a thumb drive or for running on a Laptop

first you will be locked into using basically ONLY the computer you used to install it to the thumb drive
it is NOT a "live" image

also Cent is a " SERVER" class Operating system
GREAT for running on a server in a server room
but not good for a laptop and home use

CentOS is VERY STABLE but that comes at a price
the software is RATHER OLD , tested ,fixed, patched old code
code that dose not crash
but is OLD

and runs older versions of software

the versions got LOCKED 3 years ago when CentOS 6.0 was released in July of 2011
Cent 6.5 , 6.6 , 6.7 , 6.8 , 6.9 , 6.10 will NEVER!!!!!!!!! have any major version of software newer than 2011
in 2018 it will STILL have versions of software FROM 2011

so do not expect to be able to play any NEW games ,nor any NEW apps
Also at some point and CentOS 6.5 is ALREADY THERE with Firefox 28

newer versions of Firefox newer that the LONG life Firefox 24
WILL!!!! crash all the time and for NO REASON
FF 28 is all ready there

so do not plan on using the new firefox 28 or the next 29

you will be stuck with the old version of firefox 24 LTS