I've been working with Ubuntu on my lenovo for awhile. after heavy using I started to face the black screen when I reboot. Cursor at the top left blinking with the sound of rebooting. I still see the mouse pointer. I had to hold Ctrl+Alt with F1 to work around that. After Entering my credentials, I typed in "sudo service lightdm --full-restart", so it works fine. I still face this issue every time I reboot. My question is what might cause this problem ? How do I fix it permanently ? .
Nota: I had to replace lightdm with gdm in oreder to work, although, I don't like gdm .