hi i have got stuck with a problem... i have installed ubuntu 12.04 LTS using windows installer wubi.. after the installation completed it asked for the reboot. i rebooted and for the 1st time ubuntu worked very fine. after shutting it down i cant boot it from windows boot manager. when i booted it a purple screen comes which turns into flickering screen.. so how to fix this... i have windows 7 64 bit os, radeon graphics...
Windows boot manager doesn't detect non-Windows installations.
You must use grub. If you want a user friendly method, try the boot-repair tool from Ubuntu's website (link below). Use the bootable image, and get it running on a handy USB or spare CD, since it only runs in a linux environment.
You can use this application to reinstall grub2, and repair many installation errors. Try it out, and come back if you have trouble.
If it is wubi and a video issue, Boot-Repair will not fix it. It is past the normal boot issue repairs that Boot-Repair can resolve and into video issues.
Boot-Repair can add nomodeset to standard grub, but I do not think it can do that with wubi. Alternative may be radeon.modeset=0.
From grub menu use e for edit, scroll down to linux line and change quiet splash to nomodeset. Depending on version of AMD, you probably need the proprietary drivers.