I am struggling for days to boot my freshly installed Ubuntu on my Toshiba Satelite machine (AMD A8-6410 APU with AMD Radeon R5 Graphics × 4). This laptop was bought recently, in December 2015. It had Windows 10 preinstalled and obviously it had no problems with booting, but after eliminating that nightmare operating system and installing Ubuntu 14 I could not boot my computer other than from my live USB flashdrive. A lot of people suggested me to install Ubuntu 15.10 instead, so I did, and still the same issue.
Please note that I did switched off the secure boot, I also did prioritize hard drive for booting.