I am using Lenovo Thinkpad P50 with dual booting system (Win 10 and Ubuntu 16.04), Wacom Pen support and multitouch screen. After I enabled the propriety nVidia driver (361.42?) and rebooted, I got the login loop problem. Every solution I can find would suggest to go to the console or the TTY mode to enter some commands, but in my case I cannot even switch to the TTY mode — ctr+alt+F1 doesn't work! BTW, I was trying to make the second monitor work with the nVidia driver for the nVidia Quodra M1000M card, but no luck so far.
Update: I finally got into console by chance (don't remember what works).
Tried: all the solutions on Graphics issues after/while installing Ubuntu 16.04/16.10 with NVIDIA graphics. nVidia-361 abd nVidia-364 drivers didn't work at all. UEFI has been turned off. I also uninstalled Unity (may not be complete) and installed GNOME 3.20. Tried deleting the .Xauthority file. Using Linux kernel 4.6. See comments on the answers below.
It only works when I uninstall nvidia drivers, but I need the nvidia driver for external monitor (so far no luck to use the external monitor).
Any suggestions?
One error before unstalling unity.
openConnection: connect: No such file or directory
cannot connect to brltty at :0
upstart: gnome-session (Unity) main process (2642) terminated with status 1
upstart: unity-settings-daemon main process (2632) killed by TERM signal
upstart: logrotate main process (2492) killed by TERM signal
upstart: bamfdaemon main process (2545) killed by TERM signal
upstart: Disconnected from notified D-Bus bus
upstart: unity-panel-service main process (2647) killed by TERM signal
upstart: job indicator-bluetooth failed to stop
Also, when I see the login loop happening, there is a flash of window popped out saying "Unknown tablet connected. The Wacom Inc. Pen and Multitouch may not work as expected…"
Best Answer
When you boot and the BIOS has done its work, press shift (might need a few tries to get the timing right) to open the Grub boot menu. There choose the advanced options for ubuntu. There choose the most actual kernel and recovery.
This will lead you into the recovery menu, where you can choose to be root, voila youre in a TTY now, but be careful what youre doing there is no safety net there.
Regarding that login loop you might want to take a look here since i suspect it to be the Graphics driver to cause this. (link)