Power issues?

Hi, my here is my problem:

Whenever I start my computer everything turns on fans, video card, HDD, etc. I get past the BIOS screen, hear 1 beep so I assume things are running ok, but after the BIOS screen I hear two short beeps and then computer shuts down and the screen show it is going to sleep. One thing I notice is that my LED keyboard turns off but whenever I press any keys on it they turn on, but as soon as I release them they turn off again.
Also, a minor issue that i've been wondering is that my BIOS screen and everything after that are sort of cropped and only show part of the image. I've tried moving around the Video card and adjusting the screw but images are still cropped.
Thanks ahead for any help :-)