optiplex 9020 will not power up

Replace the coin cell battery (CR2032) with a new one.

Reset CMOS via jumper.

If the problem is persisted, press and hold power supply button while press the PC power button.

If problem is not resolved, providing actual machine model/form factor and current specs would help.  Relevant information on machine prior state and/or description of events leading to issue would also help. 

Thank you for your help and support.

I preformed the three items listed and they did not resolve the problem.

The problem first started as follows.

I had a Ardunio NANO connected to one of the USB ports.

Just after loading the sketch, the fan(s?) started to spin at a high speed.

I turned off the PC and restarted it.

It would not restart. No power supply light on the rear. No LED lights on the power On/Off switch. No monitor. No keyboard lights.

I turn it on and off several times and nothing happened.

I then ordered and installed a new power supply.

It still did not come on.

I then found if I pressed the power supply reset button the fans would start but stopped as soon as I released the button.

Per your request the following is the information on the PC.

REG Model: D07S

Reg Type: D07S001

Optiplex 9020

Specifications

Table 15. Processor

Feature Specification

Processor type Intel Core i3/i5/i7 series

Total Cache Up to 8 MB cache depending on processor type

Table 16. Memory

Feature Specification

Type DDR3

Speed 1600MHz

Connectors:

Mini-Tower, Small Form Factor four DIMM slots

Ultra Small Form Factor two DIMM slots

Capacity 2 GB, 4 GB, and 8 GB

Minimum Memory 2 GB

Maximum memory:

Mini-Tower, Small Form Factor 32 GB

Ultra Small Form Factor 16 G

THANK YOU FOR YOUR SUPPORT

Brian Krupicka

The usage of IDE sketches was probably coincident and may not be the root cause.  A power surge from USB port, connected to Arduino nano, was unlikely as the device itself did not have external power.

The provided hardware information was for OptiPlex 9020 in general.  It wasn't specific to your system but I could gathered from REG Model: D07S that you have a small form factor OptiPlex 9020.

At this point, the assumption is the machine failed on its own.  You can rule out power supply since you have tested it with a new one.  Next, you may try to remove all components and inspecting motherboard for any visual damage.  Running the test again by applying power and boot machine up with only CPU installed on board.  If there is no sign of power, the motherboard is toasted.

A complete machine is value at 60 to 80 usd.  Any repair cost that is exceeding the machine value should be reconsidered.

Expanding on @Chino de Oro 's reference:  How to Run a Power Supply Unit Self Test On a Dell Desktop or All-in-One Computer  Don't let the title mislead you.  It's a way of checking internal components.  So, if you don't get the green light from PSU when pushing test button, an internal component failed.  Dell BIST Test video 

It could still come down to MB or CPU.  Check out this thread:  https://www.dell.com/community/Optiplex-Desktops/Optiplex-7060-With-No-Power/m-p/8403496#M68251