I am trying to install from a USB onto my PC with no operating system. On the first attempt, when I got to the last installation page with a loading bar, it stopped at a certain point. Each page in the installation setup takes 5-20 minutes and when I get to the last page it says something about the partition failing and it doesn't let me finish the final step. I don't know what's wrong with it.
I had similar problems once in the past and got it to work by pre-formatting the drive to ext4 before installation. You can do this with a tool such as gparted from the Ubuntu live session.
Also, if you don't have much ram, you should not select "try ubuntu" before selecting install as this option eats allot of ram and a certain amount is needed for install. (For Lubuntu, you need at least 200mB of free ram to run the installation and running the desktop eats 700mB. Also, Lubuntu uses less ram compared to regular ubuntu.) Instead, choose "install ubuntu" from the beginning.
Finally, I've found the net install iso to work better as it runs on minimal resources. See here for all PC 64 bit amd or intel processors (14.04).