Freezing when I logging in.

Hello.

I have mac mini 2012 (late) with modified RAM and additional SSD (installed using iFixIt dual hard-drive kit). Recently i upgraded to OS X 10.10 and there is a serious problem appeared.

After 3d or 4th reboot my mac start freezing when I logging in. I couldn't doing anything. Dock and Finder didn't work. I couldn't launch any application. This condition lasts for 30 minutes at least, and even after it apps launching very slow.
I tried totally reinstall OS (I formatted both HDD and SSD and splitting it for volumes again), but this problem came back.

I tried to create new user through Single User mode, and freezes finally gone after that, system worked great, but after I reboot my mac third or fourth time it started freezing again.

I hope someone could help me. Thank you.