Q: How to fix Mac Pro not start up

Hi jorge, here is an Apple Support Topic on what to do if your Mac doesn’t turn on.

https://support.apple.com/en-us/HT204267

If you have another Mac, you can try booting it in Target Disk Mode and make a backup of your files.

Share files between two computers with target disk mode - Apple Support

Then you can try following the advice in this User Tip

..Step by Step to fix your Mac

Another possibility is trying to startup by holding the command + option + r keys to your Recovery volume. If that works re-install OS X from the internet. https://support.apple.com/en-us/HT201314