Little issues while booting (MBP 13"(2014), OS X 10.10.3)

Hi there,

Sometimes I am experiencing strange behaving of my MacBook Pro 13" (2014) while booting OS X (10.10.3)

1.) Pressing Power button --> Sound --> Black screen for some time (10-20s) --> Apple logo appears --> Normal logo screen*---> Then, everything is OK. ( it is happening now,after PRAM reset, because of problem n.2 which appeared some time ago. I tried to reset SMC, but it did not solve the problem)

2.) Pressing Power button --> Sound --> Black screen for some time (10-20s) --> Apple logo will not appear (just a black screen) --> I am forced to use shortcut to reset PRAM (happened to me only two times)

*sometimes will default login screen appear with U.S. keyboard, which is not my default, after entering login information interface looks strange (password box is out of his normal place) then,after few seconds (10s) it will change to normal login screen(with my wallpaper and keyboard setup),then after typing info everything is fine

Normally, I was used to it:

Pressing Power button --> Sound --> Apple logo appears immediately --> Normal logo screen ---> Then, everything is OK. (basically everything took shorter time, than now)

I did test with Apple Diagnostic tool, but My MacBook is without any issue or error.

So, where is the problem? Software? Should I reinstall my OS X?

Thanks for help in advance!

Glutamen