Video card driver specification required.
Solution is to edit your /etc/X11/xorg.conf file to contain the correct spec values required by your card. To this you have your manual for reference. Your seller usually ships the unit with manual.
How to do it? when screen goes flicker try press Ctl+Alt+F2 or F3 or F4-6, if you are given a tty login shell screen then you are on, if not then linux is not loading at all.
At the shell terminal you should login and give password. Then to edit your /etc/X11/xorg.conf file you will only issued:
---$ gedit /etc/X11/xorg.conf
save your changes to the file (note the old one is automatically saved by the system too for easy restore if needed later).
Another way is to force login to low graphic window and use the gui enVy video card updater built into Ubuntu. At boot dialogue press Esc or F1, kernel boot options can now be entered.
Add switch to grub booting option:
This will boot you to Xwindow with a low graphic mode 600x800, there you may launch the enVy updater of ubuntu via Menu>Admin>Envy or where ever it is placed in the menus.
This updater will search the internet for the right driver (so you should be online here) then it will automatically configure the most advantageous resolution available per hardware capability.
hope this helps. good luck.