Mac Pro 5.1 new SSD not booting from USB or DVD

Internet Recovery is NOT available in ROM in most Macs before 2011 models. So you will need to explore this list of other possibilities.

When your computer was released, the way you launched the required Utilities (including Disk Utility and Installer) was to use the ones on the Release software DVD. if you have a model-specific version for your model (unlikely) or a Full Retail 10.6 DVD, you use its Utilities, boot and install that version, then use Software update to get to 10.6.8 with all updates, which is the first version that can reach out to the Mac App Store and download and install a later version.

If you have replaced the graphics card, so that it is one that does NOT have Drivers included in the release DVD, you can boot the release DVD, but you get no pictture. if you have the old card lying around, you could re-install the old card to use the Installer DVD.

10.11 El Capitan is a recommended waypoint, even if you expect to install a later version. 10.11 allows encrypted Internet connections and Mac App Store access., That makes getting later versions much easier.

The next source of Utilities is the Recovery Partition on the boot drive. If your drive spins up, even if not MacOS bootable, it may still have a usable recovery partition. To get there, try invoking recovery with Command-R or … hold Alt/Option at startup and see if the recovery partition shows as a potentially bootable drive.

Recovery Partitions up through 10.12 Sierra can be found with the Startup Manager (Alt/Option boot). At 10.13, if an SSD boot drive is used, the format is transitioned to APFS. The Recovery partition is present, but it is inside the APFS container, and the Startup Manager on an older Mac may not be able to find it.

The next source of Utilities to consider is any MacOS 10.6 or later versions on any additional drives or clones you may (or may not) have lying about, even if they are from another Mac. You can use those Utilities to ERASE a new drive, and start the installer to place MacOS on the new drive.

The next source to consider is a Time Machine backup drive. Versions from 10.7.3 or later are said to contain a Recovery Partition that could be used to ERASE a new drive and run Installer to place MacOS on a new drive. Time Machine backups created in MacOS 11 Big Sur or later are APFS format, and APFS format backup drives do NOT have a Recovery partition.

Two Mac solutions:

With certain combinations of new and old Mac, you can use Target Disk mode to repair, erase, and install on the drive of the old Mac, by treating it as a disk drive on the new Mac.

Transfer files between two Mac computers using target disk mode - Apple Support

IF you have a different Mac, you can use it to download MacOS install image, then interrupt the process and create a BOOTABLE USB-stick Installer/Utilities stick. BOOTABLE is key, because the way you will install from this USB-Stick is to BOOT the USB-stick, and use its Utilities to ERASE your drive and start the Installer. here is the article on bootable USB-Stick Utilities/Installer:

As Grant Bennett-Alder mentioned, if you can, get the old drive, and put ‘er back in.. also unless the SSD you put into your Mac Pro 5,1 is an Apple branded one , unless explicitly mentioned, you have to enable TRIM for it to work… i may get a strike out for this but we’ll see : https://kb.plugable.com/data-storage/trim-an-ssd-in-macos

if running it off a USB stick, you should be able to get to Terminal , do the TRIM thing… and see if disk Utility “sees” your new SSD. Before that, dunno… have you tried doing the usual… reset SMC then reboot and zap pram 3-4 times on startup… oh, and replace the button battery behind the video/graphics card on the backplane. It’s good for 5 years max. Goes in plus (+) side up… official replacement is BR-2032 which might be hard to find, CR-2032 will do in a pinch… i think you can google/search “reset SMC + zap pram on Intel mac” , feel free to do that, then shut down your mac pro, disconnect power cable, take off side, change battery under /behind card( you might have to temporarily remove card beforehand) , put card back properly, put side panel back, pull down lever at bak to lock it on place.. plug in power cable.. the reset SMC part you should have done already when you shut your mac pro down, disconnected power cable and let it rest for a bit.. now press power butyin on front + hold down Apple+ option+p+ r keys together for 3-4 chimes then let go, Plug in your bootable usb stick and hold down the “option” key… that ought to get you the startup manager… the usb stick should be one of the choices, .. well, i tried

john B

what graphics card is installed?

Mojave REQUIRES Metal-capable graphics card with Mac Boot screens.

do you still have the old drive?

It's a LOT easier to install MacOS on that Mac when you are already running MacOS.