Mac Pro 2013 just blink power button not booting

RE: the 42 lb silver tower Mac Pro and the dark cylinder Mac Pro.

The power button blinks, often in patterns of three, when there is not enough WORKING RAM memory to start up. This usually occurs because DIMMs have failed, and you are down to too few working modules to start up.

With the power still on, remove the side door and observe which DIMMs have red LEDs lit next to them. These all tested BAD.

On the MacBook Pro (any of over 50 models) the failure is the same, but the problem may be slightly different (such as dislodged modules) and different resolution. Also, there are no LEDs to indicate which modules failed.

It powers on and makes noise? If yes, try to press command + option + P + R until it tries to but two times, see if it works again, it can be problem with configuration and this command will clean the PRAM of your Mac. Detail: you have to press and continue the pressing or be pressing very fast, has a certain moment to press the buttons. Good luck!

Possibly a memory problem? Happened to me last week when I tried to install new memory that wasn't compatible with the memory I had in there.