I have a really strange problem on my Ubuntu (and on my whole computer now). Some days ago, my computer began to take a very long time to boot (2-3 minutes). Thus, I reached out for help in order to see where the problem came from. I solved it by reinstalling my nVidia drivers, and going from bumblebee to prime. It worked, my computer booted faster, very well. First thing I did was however to select the Intel card as my principal graphics card.
Today, I wanted to play some games, so I tried to revert it to the nvidia card. I got the same problem as was already described here : Can't switch anymore from Intel to NVIDIA GPU . I tried one of the solutions, it seemed to work (I was able to switch), but when I logged out, my computer just hang. I reconnected using tty2, and forced a reboot. After that, I was unable to log into X again. After a few tries, I decided to remove the prime drivers and get back to bumblebee.
Now for the strange part : my graphics card seems to have completely disappeared from my system. It is not recognized by my Windows 8.1 anymore (before my troubles on Ubuntu, I had no problem with my graphics card on Windows). Furthermore, when I installed bumblebee, it complained that I had no nVidia graphics card on my system. There is also only one listed VGA device on lscpi : my integrated Intel chip. https://askubuntu.com/users/272018/user5288 seems to have had the same problem, but it was never resolved it seems. Does anybody know how to resolve this ?
Btw, I'm running Ubuntu 14.04 on a Dell Inspiron 7720 with a nVidia GT 750M (before it disappeared...)
Thanks in advance.
Edit : problem finally solved. Reinstalling the drivers did not work at first. However, I've got an other advice on a different forum : unplug the power supply, remove the battery, wait for about ten seconds (I also pressed on the power button for ten seconds, doesn't know if it helped). After this, I booted, the graphics card was recognized under Windows. I reinstalled the nvidia drivers and now everything works fine ! Thanks :)