Problems Adding Plugins

Hello Everyone, I can´t install any plugin. I copy the uncompressed folder on the plugins folder, but it does not appear in the plugins list.
I use Omeka with XAMPP.
Any help?
Thank you

Just to clarify, do they not show up at all, or do they appear with a message saying something like “Not a valid plugin”?

They don`t appear at all. I tryed with many plugins. I have only 3 by default with the installation

Probably a issue related to rights. The owner should be apache or www-data (set it according to your install) and folders rights should be “555” and files rights should be “444” (or 775/664).