While booting from USB, after clicking "Try Ubuntu", computer freezes
It could be a problem with your graphics card, because Ubuntu uses those new open source drivers.
Edit the startup options on "Try Ubuntu" (If you use UnetBootin first highlight "try ubuntu", then press tab (or was it e?). On pendrivelinux I'm not sure where you can edit those). And insert nomodeset next to the other boot options. Then boot with this option.
It should boot up successfully if the graphic driver was the problem. You then have to install the proprietary drivers (after Ubuntu installation).