This problem has a couple of facets so hopefully it won't seem to messy.
I have been running a wp e-commerce site for the last few months, during which I have spent hundreds of hours adding products.
Basically my site was running extremely slowly so I decided to delete all my plugins and see what happened. For some reason when I clicked deactivate it would not do anything and the plugins kept running so I was unable to delete them.
Consequently I went to the wp-content/plugins folder and manually deleted all of the plugins from there. When reloading my site in the plugins section a series of error messages like this:
"The plugin easing-slider/easingslider.php has been deactivated due to an error: Plugin file does not exist."
appear in the plugins section (for a few plugins). That is one of my problems.
The other is that I did the same thing for the themes, I manually deleted them from the ftp and uploaded the basic WP 3.5 themes folder and the one I have been using (Blackbird). Unfortunately this has resulted in my site coming up as a blank page and an error massage on the backend:
"ERROR: The themes directory is either empty or doesn’t exist. Please check your installation." on the Dashboard
and "The active theme is broken. Reverting to the default theme." in Themes.
The installed themes do appear but cannot be activated.
I appreciate that this is something of a meandering problem but I have spent months adding products to this site and now it has stopped working entirely I am very concerned. I hope someone can help!