After doing "apt-get upgrade" my pc only boots into command line. If I try "startx" it tells me that there is a "symbol lookup error: /usr/lib/xorg/modules/extensions/libglx.so: undefined symbol: LoadExtension"
I have a gtx 750 and I installed the nvidia driver. I really do not know what to do with this or how to solve it.
Did you use the noveau drivers beforehand? If you were running the FOSS drivers first, then installed the proprietary drivers & rebooted, you have 2 conflicting drivers.
Sounds like the last update provided broken drivers, one fix is to wait for a patch from nvidia & re-update, or "fallback" to noveau. If someone has a better solution i'd also like to learn how.
Just an idea, I'm not an expert with linux but you should apt-get purge your driver and then re-install. It's probably an issue with the new driver conflicting with your old one. Purge will clear configurations and remove only uninstalls it. If this doesn't fix it, report it.
Yeah normally this works, if the kernel has been updated or one of the headers, it more than likely will break it, just do as said here and you should be okay :)