This question is an exact duplicate of:
I'am trying to install 13.04 via usb; however, when I boot to grub and press install Ubuntu, my screen will flash repeatedly between white and purple and will no proceed any further. So I pressed "e" in the "install Ubuntu" option and changed "quiet splash" to "quiet splash nomodeset" that made me able to recognize the colors in the typical installation process in Ubuntu, but everything seems to be piled up in the upper part of my screen, making it impossible to proceed in the installation. My computer is a Toshiba Satellite S855-S5170 and I attribute this problem to the dual graphics card (AMD Radeon HD 7670M Graphics 2GB DDR3). Thanks for taking the time to help me.
I managed to install Ubuntu by disabling "Virtualization Technology" in my BIOS (which I believe let's me operate several OS's) and changing in grub2 "quiet splash" to "quiet splash nomodeset". However, when I reboot after installation (I installed the third party software), my screen will start blinking again. So I again changed the command "quiet splash" to "quiet splash nomodeset" but now I end up in what I believe is the terminal. But I do not know how to proceed from here. Again thanks for helping me.
I changed 'quiet splash' to 'nomodeset' as it was suggested, but I did the same thing (i end up in the terminal) Then (inside the terminal) I tried 'startx' but it says that '[KSM] drm report modesetting isnt supported' 'fatal error: no screens found' What can I do now? Thanks for the support.