Cannot activate/deactivate plugins or change WordPress Settings

I cannot activate or deactivate any plugins. When I try to activate or deactivate a plugin WordPress does refresh the page and there’s a notification that a plugin was succesfully activated/deactivated but they haven’t really been activated or deactivated.

If I rename a plugin’s folder the plugin will break and deactivate but if I change the name of the folder back the plugin activates again and I cannot deactivate it.

I have tried repairing the database (by adding define('WP_ALLOW_REPAIR', true); to wp-config.php and going to mysitename.com/maint/repair.php and clicking repair database) with no luck. It does say that all tables are ok but this does not solve the problem. I have only shell access to database (no PhpMyAdmin).

If I go to updates page in wp-admin and choose to reinstall WordPress the plugins I have tried to activate or deactivate earlier appear to be activated or deactivated after reinstalling WordPress. But having to reinstall WordPress every single time I want to deactivate or activate a plugin is a bit too much if you ask me.

I have no access to server error logs and my host is of no help in this situation. I have contacted my host but they stated that there is norhing in the error logs and this problem is caused by my theme or my plugins and that they cannot help me. I just can’t understand this because I have the exact same plugins and theme working on another site located on another server. Could my WordPress install be corrupted? How can I fix it without losing my posts and media library content if this is the situation? My site is has little over 100 authors now and about 1000 posts and same amount of comments.

And in addition of being unable to activate/deactivate any plugins I also cannot change any of the WordPress Settings. If I try to – for example – change my sitename in General Settings, WordPress will state that settings were saved but the sitename did not change. It’s the same for every other setting. Any of my plugin settings aren’t getting saved either. And I might also add that if I go and reinstall WordPress from the updates page the settings that hadn’t been saved before seem to have all changed according to what I tried to do before reinstalling WordPress.

I can however still publish posts and add users or change user settings and manage pages and upload files to media library.

Any help would greatly be appreciated! I have been dealing with this problem for quite a few weeks now and I just haven’t found any solution.

My site has the newest WordPress version (4.3.1) installed and all the plugins are also updated to their newest versions. I do have W3 Total Cache enabled but disabling it (by changing the name of the plugin’s folder) did not seem to help either. And I did try manually reinstalling WordPress also (by replacing pretty much everything except the wp-content folder with new files from a fresh install) but this did not help either.