Help! Installation problems

I'm installing Ubuntu on my computer. When I boot up, I select "install Ubuntu" on the splash screen. Then, after loading, I have a screen with no GUI. I type in "startx" But I don't get GUI. I click Ctrl Alt F5. Someone told me what to type in. Then, it installed, but Ubuntu somehow wasn't loaded on to the computer.

My first question: What command do I type in?!?!?!?!?!?!
My next question: How do I keep Ubuntu loaded on the computer?

THANK YOU x 1 Billion to anyone who answers my questions.

Do md5sum on your iso. Burn new CD at 4x.