I would like to say a BIG thanks to Simon for troubleshooting this issue for me. I emailed my log file and he came back with this prompt response.
Your issue is different from the missing My Pictures folder. It looks like you do not have write permission to the Lightroom Presets folder for your computer's login account.
On Mac, it is under "/Users/<your account name>/Library/Application Support/Adobe/Lightroom". On Windows, it is under C:\Users\<your Windows login account name>\AppData\Roaming\Adobe\Lightroom". If you still have an earlier version of Lightroom running, you can bring up the Lightroom preference dialog, under the Presets tag, click on the "Show Lightroom Presets Folder..." button.
Make sure you have read/write permission to the "Application Support/Adobe"/"AppData\Roaming\Adobe" folder and its subfolders.
My LR 5.4 is now up and running on my main machine thanks to this resolution. Hopefully, this will prove useful to some of you.
A side note: I was using Dropbox Folder Sync on my LR presets folder so this may have been the root cause. I'm sure that that there are others of you out there using this application to backup your presets
