@ForceHSS
The only that I did before it happened was the ...installation

. This issue appeared when I clicked "Goto AdminCP" just after a successful installation. So no plugins, no styles installed. I mean 3nd party mods/styles. Just vB core.
@Zachery
Even if I'll do a fresh installation right now, I don't believe that it's a server's or PHP version issue as I installed it in another directory on the same domain and it works.
But thinking in a funny way, I think that it will be good idea to keep it as is. Should be the most secure installation

If a hacker needs to have 3 tabs open (frontend, modcp, admicp) to be able to work in admincp, is really secure. I forgot to say that closing the modcp window and clicking any link in admincp shows again a blank page.
--------------- Added [DATE]1412258725[/DATE] at [TIME]1412258725[/TIME] ---------------
Finally I upgraded to 5.4.33 and now everything works fine. Thank you all.