I had one problem getting Ubuntu 14.04 to install on a Dell Inspiron 5000 series. Booting from the USB was no problem – hit F12 at startup to go to boot menu, and chose to boot from the USB drive. I didn’t have to disable Secure Boot or UEFI mode.
However, after selecting “Try Ubuntu”, all went blank. When I tried a second time in Legacy boot mode, I got a more helpful error message:
ACPI PCC probe failed
A quick google suggested this was a problem introduced Ubuntu 14.04.3. Some scary sounding fixes were suggested, but I took the easy option of downloading the 14.04.1 iso instead, which installed fine.