This question is an exact duplicate of:
I did 'apt-get dist upgrade' and upgraded it. It was done 100% but it asked me to open the upgraded packages so I did yes and I went out for a work for 1 hour. But after I came I saw that my pc was on standby mode. So I pressed some keys but it didn't start so I restarted my pc and I started Kali bit after inserting username and password it gave a white screen and when I tried to open terminal it opens and after a second it again took me to inserting username and password point.