Installed Ubuntu on iMac 2009 4GB Ram 2.4 GHz Intel Core 2 Duo

[kalpana]

I installed Ubuntu from a USB drive. It asked me for my name and info, went through the install. It said to "restart" the computer, I did. then it said to with draw the media and hit enter. Again did that. When the computer restarted it makes the sound of restarting then the screen is just white. Nothing happens. After a few minutes it restarts itself and again nothing happens.

I have re-installed it twice.

Any ideas on what I can do? Should I re-install again?