Struggling reinstalling El Capitan on Mac Pro 2008

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 version that can reach out to the Mac App store for the first time and download and install a later version.

10.11 El Capitan is a recommended waypoint, even if you expect to install a later version, because it has an improved Mac App Store 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.

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:

What you need to create a bootable installer

• A USB flash drive or other secondary volume formatted as GUID partition Map, Mac OS Extended, with at least 14GB of available storage

• A downloaded installer for macOS Big Sur, Catalina, Mojave, High Sierra, or El Capitan.

from:

How to create a bootable installer for macOS

Create a bootable installer for macOS - Apple Support

NB>> if you name your incoming USB stick exactly MyVolume, you can copy and paste the very long Terminal command from the article directly into the Terminal window, without having to change anything.

One of the simplest things a Mac can do is boot with the Option key held down, PROVIDED the keyboard is connected to a USB port on the chassis, not on a display or other USB Hub.

The Mac should, if no hardware problems, draw a gray screen, show a wait cursor, and slowly, over a period df minutes, add an icon for every potentially-bootable Volume it can find by brute force. No drives or any contents need to be functional to get the gray screen and likely the cursor. if you don't get this, your Mac has some remaining issues.

When the wait cursor transitions to the regular cursor, it has finished one pass of looking around. if you add a CD later, it will look around again.

the trick to opening the built-in CD drive is to press slightly in and down to open the decorative door, then apply a bent paper clip into the tiny hole in the face plate of the drive, which will pop it open about a quarter inch, then it can be dragged open.

If you have not returned your memory to a more normal arrangement, the memory could be running very slowly.

If you get a solid Apple that is NOT inside you Mac at cold start, and can only appear when loaded in the first 'blob' of software off a drive. Backup drives may have a recovery partition., MacOS High Sierra makes it more difficult to completely erase a drive, hiding the recovery partition and only showing the MacOS Volume by default, not the entire device.

That Mac may support the startup shortctut C (for CD).