I’m assuming this is a local install since you’re using MAMP. Is it installed on OS X or Windows?
If you’re using a Windows computer you could try doing a system restore and it may restore the upgrades you made but I’m not sure if that would work or not. You’d want to make sure you hadn’t installed lots of other programs on your computer or done major upgrades since you made the changes you’re wanting to remove by doing the system restore.
As far as the plugins go I’m not sure why you copied in a backup copy of MAMP. If your plugins weren’t working I believe you’d only have needed to copy an exact backup of your plugins folder (not just an unzipped plugin folder) and you wouldn’t have needed to do anything with MAMP. Otherwise you could uninstall each plugin and then reinstall them one by one.
When you copied the MAMP backup folder over the previous copy did you use an unzipped copy of the original MAMP download files? The install process for many programs makes changes to file/folder permissions and so forth. So if you just copied the unzipped download files those changes wouldn’t have been made during the install process (this is true for plugins too). So that could cause the error you quoted.
In regards to phpMyAdmin did you pay for a MAMP Pro License or just use the 14 day free trial? phpMyAdmin is only available in the Pro version so if you used a trial it may have expired.
On the MAMP site it says:
…if MAMP is no longer needed, just delete the MAMP folder and everything returns to its original state (i.e. MAMP does not modify any of the “normal” system)
You could try doing that and then reinstalling MAMP. Otherwise maybe you could try installing MAMP without deleting the MAMP folder and it may detect a previous install and give you an option to repair or reinstall MAMP.
If you’re on Windows I use WebMatrix for my local installs and it has a really easy way to install WordPress. It’s a free web development tool that lets you do similar things to what MAMP gives you access to. You can find out more at: https://www.microsoft.com/web/webmatrix/
You don’t have to scrap all your work on your site. You can still backup your existing WordPress database from the admin panel within WordPress (Tools > Export). I prefer doing it through phpMyAdmin but you can always do it that way. Then you could reinstall WordPress and import your database from the same location in the WP Admin Panel. That way you wouldn’t lose all the other work you’ve done.
Hopefully some of this helps.
