Having trouble installing El Capitan on my Mac Pros (early 2009 and mid 2012) machines

"Having Trouble" does not give Readers anything to start with.

What do you do, and and at what stage do things happen that lead you to think you are, "having trouble" ??

What PCle cards are installed? CalDigit USB cards will cause that problem.

https://forums.developer.apple.com/thread/18470

There may be other cards or peripherals that can also cause the crashed. Tru disconnecting everything not really needed.

If you can't start up and log in in the usual way, try in safe mode.

During startup, you’ll see a progress bar, and then the login screen, which appears even if you normally log in automatically. You must know your login password in order to log in. If you’ve forgotten the password, you will need to reset it before you begin.

Log in as an administrator to carry out these instructions. If you have only one account, you are the administrator.

If you don't see any reports listed, but you know there was a panic, you may have chosen Diagnostic and Usage Messages from the log list. Choose DIAGNOSTIC AND USAGE INFORMATION instead.

Safe mode is slower than normal, and some things won’t work at all.

Note: If FileVault is enabled in OS X 10.9 or earlier, or if a firmware password is set, or if the startup volume is a software RAID, you can’t start in safe mode.

If you're able to log in, launch the Console application in any of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad and start typing the name.

In the Console window, select

DIAGNOSTIC AND USAGE INFORMATION ▹ System Diagnostic Reports

(not Diagnostic and Usage Messages) from the log list on the left. If you don't see that list, select

View ▹ Show Log List

from the menu bar.

There is a disclosure triangle to the left of the list item. If the triangle is pointing to the right, click it so that it points down. You'll see a list of reports. A panic report has a name that begins with "Kernel" and ends in ".panic". Select the most recent one. The contents of the report will appear on the right. Use copy and paste to post the entire contents—the text, not a screenshot.

I know the report is long, maybe several hundred lines. Please post all of it anyway.

If you don't see any reports listed, but you know there was a panic, you may have chosen Diagnostic and Usage Messages from the log list. Choose DIAGNOSTIC AND USAGE INFORMATION instead.

In the interest of privacy, I suggest that, before posting, you edit out the “Anonymous UUID,” a long string of letters, numbers, and dashes in the header of the report, if it’s present (it may not be.)

Please don’t post other kinds of diagnostic report.

When you post the report, you might see an error message on the web page: "You have included content in your post that is not permitted," or "The message contains invalid characters." That's a bug in the forum software. Please post the text on Pastebin, then post a link here to the page you created.

If you are running other OS versions, and the CalDigit card works fine with them, I don't believe you need to pull the card. You just can't use the drivers for earlier OS versions with El Capitan: so you can't upgrade an existing system to El Capitan if it has the CalDigit driver installed. I ran into this with my 2010 Mac Pro, after I installed El Capitan clean and then installed a CalDigit Yosemite driver. Big mistake. But without the driver, El Capitan is fine with the card itself: however, the card is invisible to the system, and no drives attached to it can be used, obviously. Not a big deal for me, but if you want to have El Capitan on every drive, you won't be able to use the CalDigit card.