If the power light is blinking amber, the computer is receiving electrical power, but an internal power problem might exist. You may have a bad PSU. Check the diagnostic lights on the back.
I have a Dell Dimension 4500 desktop with 15" LCD monitor. I turned the CPU and monitor off in the morning. When I turned the system on in the evening, the CPU powered up but the LCD remained blank and the power light is blinking; it blinks in groups of three.

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