I've got an issue with booting, and when the system tries to start x, it hangs and only a cursor is displayed. It is not possible to switch to a command prompt or SSH in at this stage.
Is it possible to change something in the config.txt to boot only into CLI so I can investigate the problem?
I think a number of people have reported this problem recently after relatively innocuous sounding configuration changes or installing software. I can't diagnose it for it you, however...
Is it possible to change something in the config.txt to boot only into CLI
Presuming you are using Raspbian jessie, there should be something you can add to cmdline.txt. You can override the default target of systemd to use a non-graphical target:
systemd.unit=multi-user.target
Again, that's cmdline.txt, not config.txt. And very important: that file should contain one line. No more. It can be quite long and you should add that to the end separated from the previous parameters by a space.
There are some other possibilities here but try that one first.
