Weird Cut Out - No Idea what is wrong

I do not know what is wrong with my computer. It has been working fine for over a year. The other day after taking it to a friends house, (which I do regularly) I went to set it back up. Upon turning it on, during the start up process, the display was blinking every few seconds and each time it would you would hear the air sound of the CD drive spinning that I hear every time I start the computer up. After I got to the user screen to log on, I typed in the password and signed in. While the desktop was loading the computer blinked again and the computer just shut down. So I don't know if this is a problem with the graphics card, the processor, or somehow the power supply? Like I said it has been working fine for over a year so the problem is something that had to have happened recently. IDEAS???!!!!