Where to look when the system crashes or something else horrible goes down?

My Linux Mint workstation is acting funky, it appears to be logging me out randomly, though I'm guessing what's really happening is that the X desktop is crashing. Maybe.

How do I troubleshoot this?

I'm not sure which log file to look at. I tried looking at dmesg and Xorg.log in /var/log but I'm not sure what to look for. Not to mention there are no conventional timestamps, but a string like [ 0.416674] and I have no idea what that means.

These four files are your best bet.

/var/log/Xorg.0.log

/var/log/Xorg.0.log.old

~/.xsession-errors

/var/log/messages

After doing some research, seems like (for whatever reason), any recent X crashes show up in /var/log/Xorg.0.log.old