The OptiPlex 755 offers energy-efficient performance, stability and choice in a mainstream business desktop.

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Computer fails to come on.

The computer was shut down and the power turned off. When I turned the power back on the computer would no come on. Power cord is ok and has power up to back of machine.

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Hi @bultaco Do you get any light indication, blinking or solid, green or amber, in the power button and are there any diagnostic LEDs showing, on the front of the PC?


No lights come on. Nothing happens. Maybe power supply?


Same here no lights when I plug my power adapter in


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Try one of the the following to prove whether the fault is in the PSU or the motherboard.

a) Here is a link which describes how to perform a power supply self test for an Optiplex 755. It does depend however if you have an Energy Star 4.0. PSU installed. Read the section on power supply self test and then click on 341 at bottom of the page in the link to go to the next page to see more on what to do.

b) Here is what you can do if you cannot do the above test.

1.Unplug the PC from the AC power.

2. Open the case and disconnect all the cables that come out of the PSU to the various connections in the PC like the motherboard, HDD, ODD fans etc. Take a picture or make a note of all the connections before you do this.

3. There should be a 24 wire cable going from the PSU to the motherboard. On the cable connector for these wires find pin 16 (see image - it may have a green wire but maybe not, it can vary as to the colour used.) Using a paper clip connect pins 16 and 17 together by opening the paperclip and inserting one end into pin 16 hole and the other end into pin 17 hole of the connector of the cable going back to the PSU.

Once you are satisfied that the motherboard and everything is is disconnected from the PSU, plug the AC power cord back in and switch on the AC. If the fan in the PSU starts up it is a good sign that there is life in the PSU. If you have a DMM (Digital MultiMeter - Voltmeter function) you can measure the voltage coming out of the PSU on the 24 wire cable as per the image. If these are within tolerance then your PSU is OK but unfortunately your motherboard isn't.

If nothing happens when you do this then your PSU is faulty.

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When you press the power button do you see the light turn on and if it does then do you see the dell logo on the screen. If you do not see the light turning on then it's most likely the power supply.

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