My compaq dc5100 machine has this problem. It powers on for less than 5 seconds and then shuts down leaving the power LED on. I have to unplug the power cable for at least 10 seconds to be able to power it on. When I unplug the CPU power, it gives me 4 beeps (with red blinking on the power LED, simultaneously) and pauses for 2 seconds before it continues to beep and blink. What could be the problem and how can I solve it?