Sign-in time too long (Win 8.1)

Two days ago I received quite a strong new Win 8.1 computer (with SATA drive).
I have opted for a LOCAL user only without a password.
The boot process was extremely fast: the computer turns-on to the blue log-in screen in few seconds; and then pressing Enter the signing-in process was almost immediate.

Then, a bad thing happened: I was lured by Microsoft to sign-in with a Microsoft account.
Then, signing-in to my computer with this MS account (and password) took ages; I mean, something like a full one minute the computer was trying to sign-in until eventually succeeding.
Understanding my mistake (why would I want an MS account?) I decided to disconnect from my Microsoft account, and return back to my nice local user.

But now, the long waiting time to signing-in (even without a password, and with an automatic log-in) still remains: I wait like 25 sec when the blue screen and the white dot circulate repeatedly until my account is signed-in.

What is going on?
Help me!