I tried to update manually (by replacing the wp-admin, wp-includes & core files) but that resulted in the plugins page (/wp-admin/plugins.php) & wp-admin/update-core.php pages coming up as blank pages.
Any ideas how I got myself into this mess & how I can get out of it?

HI blogbeauties,

Is there any chance at all that you have a backup?

What version did you start from? If it was just a minor upgrade you could possibly upload the older version again and get it back to where it was. Then try the upgrade.

Before you do anything make a backup of your data base. If you lose that you're really in trouble.

Let me know if you can back up a step or not.

Ed

I reverted to my last backup, but the update page & plugin page are still not coming up... now it is not a completely blank screen however. It is a partially blank screen. I attached a screen shot for you.

ok. figured it out.

This was a helpful article: weblogtoolscollection.com/archives/2010/...ite-screen-of-death/

I basically did this:
How to deactivate all plugins when not able to access the administrative menus?
Sometimes it may be necessary to deactivate all plugins, but you can't access the administrative menus to do so. One of two methods are available to deactivate all plugins.

Use phpMyAdmin to deactivate all plugins.

In the table wp_options, under the option_name column (field) find the active_plugins row
Change the option_value field to: a:0:{}
Or reset your plugins folder via FTP or the file manager provided in your host's control panel.

Via FTP or your host's file manager, navigate to the wp-contents folder (directory)
Via FTP or your host's file manager, rename the folder "plugins" to "plugins.hold"
Login to your WordPress administration menus (/wp-admin)
Via FTP or your host's file manager, rename "plugins.hold" back to "plugins"

... and then figured out it was JetPack.

Very resourceful! Nice job.

Cheers,
Ed