Why does my PS3 power itself down after 2 seconds by itself?

When I turn on my PS3 Super Slim, it turns on for about two seconds, and then acts as if I had just pulled out the power cable after making a very light *beep* sound that is almost inaudible. When I pull out the hard drive, this sound is not played, but the same thing happens. You can also see the lens come up a small amount upon starting and go back down with a *click* when the PS3 shuts off. This sound is quiet enough for the fan’s whirring to block it out, but when you are close enough, you can hear it. This originally happened occasionally, but soon would not power on for more than 2 seconds. If I put it in a pixel-perfect position, it stays on for about 20 more seconds, then just does the same thing again, but even this happens only occasionally. The light goes out completely when it powers down, and when the power button is pressed, it turns red with a *beep* and then green with another *beep* after pressing the button again. Could someone tell me what the problem is and how to fix it? Thank you!