Early 2009 Mac Pro

Hal Frederick wrote:

I have a Mac OSX 10.11.6 dmg on USB to install but every time I start the Mac Pro in option it does not recognise the USB, it displays recovery but not the USB disk and I have tried several USB disks. At this point I have a Mac Pro with an empty startup disk and need help!

Having a .dmg file stored on a USB stick does not make it bootable. In order to create a bootable macOS 10.11 USB installer, you need access to another compatible Qualifying Mac in order to use the instructions in this Apple article to create a bootable macOS USB installer:

Create a bootable installer for macOS - Apple Support

A Qualifying Mac for macOS 10.11 is generally one from 2008 to 2015, but you can use the information in this article to confirm compatibility:

https://eshop.macsales.com/guides/Mac_OS_X_Compatibility

If you don't have access to another compatible Qualifying Mac, then you will need to use an OSX 10.6 Snow Leopard upgrade DVD so you can get a working OS on this system. Then you can download the macOS 10.11 installer (links in the Apple article for creating USB installer) and upgrade macOS from 10.6 to 10.11. There are no other reliable methods of creating a bootable macOS USB installer.

Dunno, Harold, try the basics first : https://www.macworld.com/article/224955/how-to-reset-a-macs-nvram-pram-and-smc.html… you should do zap pram at least 3 times on startup… also, there’s a coin type battery behind the video/graphics card which affects startup, especially if it has died which after 5 years it probably has. It goes in plus side up, and is a BR-2032 but CR-2032 will do OK..,

John b