The power switch does not work.

@joyy3 check the diagnostic LED’s

Logic Board Diagnostic LEDs

The Mac Pro logic board includes a set of LEDs to help service providers troubleshoot the computer. The LEDs are located on the logic board between the two DIMM riser card connectors. LEDs 3, 4, 5, and 6 are normally off and will automatically illuminate if an error occurs. To read LEDs 1, 2, 7, 8, and 9, you must press the DIAG_LED button, which is adjacent to the LEDs. To press the DIAG_LED button, use the nylon probe tool

LED 2 is of interest

LED 1 Sleep

LED 2 Standby or Trickle Power

Normally on when DIAG_LED button is pressed.

If LED 2 is not on, the symptom would be that the computer won’t power on.

• Troubleshooting:
• Check AC cord is connected to a working AC wall outlet.
• Reseat AC Plug.
• Check connections of power supply cables to the logic board.
• Check power supply cable connections at power supply.
• Replace power supply

Power-on LED illuminates when pressed in, but goes out when button is released, there is no boot tone or video, but you can hear a small click

• Check diagnostic LED 2 for trickle voltage from the power supply. Refer to “1. Power Supply Verification” in this chapter. If verification fails, replace power supply.
• Verify that the processors are properly seated. Check diagnostic LED 3 and/or LED 4 2.
• Verify that the processor mounting clamps are properly tightened. 3.
• Replace the power supply.4.

Power-on LED illuminates when power button is pressed but fans do not spin (or spin only momentarily) and there is no boot tone or video

• Reseat video card. (Make sure video card is fully inserted in connector and end of card is 1. secured by the connector latch.) For video cards that require power cables, check that they are connected.
• Reset logic board. Refer to “2. Resetting the Logic Board” in this chapter.
• Verify power supply cables are fully connected. 3.
• Check diagnostic LED 3 and/or LED 4 for processor connection. 4.
• Reseat processors and check for bent pins. 5.
• Check diagnostic LED 2 for trickle voltage from the power supply. Refer to “6. Power Supply Verification” in this chapter. If verification fails, replace power supply.
• Replace logic board. 7.
• Replace processor.

Power Supply Verification

To power on, the computer’s logic board requires “trickle” power. If the system fails to power on, first reset the SMC as described in this chapter. If the computer still doesn’t power on, follow the procedure outlined below to determine whether the issue is related to the power supply.

Verify trickle power

Diagnostic LED 2 indicates the presence of trickle power required by the logic board to begin the startup process.

LED 2 should be yellow when the DIAG_ LED button is pressed, indicating that trickle voltage is present.

Verify Power Supply Is Providing Power

Diagnostic LED 8 indicates that the main power is OK and within regulation.

Plug in AC power cord, and press the power-on button on the front panel.

LED 8 should be green when the DIAG_ LED button is pressed, indicating that the main power is OK and within regulation.

If diagnostic LED 5 and LED 6 are both solidly illuminated at power up, improperly seated power supply cables could be one cause of this behavior. Check all power supply cable connections to ensure they are properly seated.

Let us know what you find out.