Cannot Login To Your WordPress Site/Blog?
Cannot Login To My WordPress Site
If this ever happens to you, don’t panic, don’t go changing your password. Take a deep breath, go get your coffee/tea/soft beverage of choice and prepare for an almost mind numbing experience, ( the harder beverage of choice can come later, you’ll enjoy it more then)
In more cases than not, the reason you cannot login to your WordPress site/blog is caused by a plugin. I said “take a deep breath etc” because if you have many plugins then this little job can take some time.

Firstly to be able to login, go to your FTP client and change the name of the plugins folder to anything you like as long as it is not just ‘plugins’. I changed mine to oldplugins.
Now go back and try to login, you should have access now. In the Plugins section you should have error messages for all your plugins telling you that they cannot be found and have been deactivated or something to that effect.
Next make a folder on your desktop or wherever you like and call it ‘oldplugins’ then download all the plugins from that folder on your site.
Make a new folder in your wp-comments called, you guessed it, plugins.
Now the ‘fun’ begins! Upload each plugin that is in the ‘oldplugins’ folder to the new ‘plugins’ folder, one at a time.
So what you do is:-
Upload plugin.
Activate plugin
Log out
Log in
If you get back into your site, that plugin is fine.
If you find that the plugin from your folder needs upgrading after you upload it, don’t do the upgrade before you log out and then in. If the logging out and in works, then upgrade the plugin and try the log out and in again.
Do this for every plugin and you should find that after activating one of them, you will not be able to login. That one till be the culprit.
Go back to your FTP client, delete it from your system and if it is for a function that you cannot live without, there is probably another that will perform the same or similar function.
This incompatibility can happen after installation of a new plugin or an upgrade of a plugin too, could be the WP version and the plugin version not getting along.
I did think that the way the auto upgrade for plugins in the 2.8 version was great and it still is but from now on I will only ever upgrade one plugin per login session and make sure I can log out and in again.
Thank goodness all is back to normal, well normal for me, could be different for you