Macbook Pro half split black screen at login
At login my Macbook's screen appears for its biggest part to be black, like if it has been shifted or split in two, while the remaining part of it has some color of what seems to have been left from the original log in screensaver. Once i insert the password and the login is carried out, there is no problem at all, the desktop and the screen go back to normal. I have tried to reset both the NVRAM and the SMC according to the official guidelines but nothing changed. Could you please suggest what else I could possibly try out? Thanks in advance
MacBook Pro 13″, OS X 10.11