I would suggest this.
Remove the live cd and reboot. When you get the grub menu, interrupt the timer and press the specified key to edit the kernel arguments. Add a space then 3 to the end of the line. Then hit return. This will boot to run level 3 which is before X is running. You will have a command line login, so login as your user then take a look at the contents of ~/.config
You should find the settings in there.
Change the relevant settings, save the file(s) and then try running startx. If it's fixed, great, if it's not then you can reboot and try the sequence again. It does not need a reinstall to fix this.
If you need more help then try asking here
Alternatively, you could login to run level 3 as root, create a new user, logout then reboot. Login as that new user and check that everything works as required and copy the contents of ~/.config into the original users home directory, remembering to change the ownership of the files. You would need to be root to copy the files across, so run it from a terminal.