iMac login window doesn't react for a long time when waking up my mac

I have several problems with my iMac. I have an iMac 27" Late 2012 with an Intel Core i7 3,4 GHz, 16 GB Ram, 3 TB Fusion Drive, a NVIDIA GeForce GTX 675MX (1 GB Ram) and OS X Yosemite 10.10.2.

Every time, I wake my iMac up from screen locked (⌃ + ⇧ + ⏏) he shows the typical "spinning beachball" for a few minutes, until I can enter my password.

Another problem is that, when I open System Preferences and click on "Mouse" I also had to wait a few minutes, until I can change the settings. While waiting, he does also not show the Animation on the right side. The animation becomes visible, after he stopped showing the spinning beachball. While this, only the System Preferences are stuck. All other apps are working properly and also the system is working and does not show the spinning beachball, while I wait for the preferences to load. The spinning beachball is only visible, when my mouse pointer is over the system preferences. Opening the Mouse Preferences takes 2 and a half minutes, which is in my opinion too long to be a normal loading process.

And now the crazy thing. When I lock my screen with the key combination (⌃ + ⇧ + ⏏), it also takes a few minutes, until the screen is black and locked. But when I lock it with clicking on the lock in my status bar and then clicking on "Lock screen", the locks the screen immediately. As I am not allowed to post pictures here is a screenshot of the lock in the status bar and the option below, that I click, to lock the screen immediately: http://ift.tt/1J8DzS9.

How can I solve that problem? The problem existed first after I installed OS X Yosemite 10.10, but the 10.10.2 update didn't solve it. Resetting my iMac didn't work too.

Thanks, iComputerfreak