I had installed my Linux 5.1 couple of months back and was working on it smoothly. I also had Xwindows installed and X-Windows console login used to comeup automatically on reboot. But then yesterday I ran Xconfigurator to set some monitor resolution and mistakenly set the monitor refresh rates to wrong values. Now if I reboot, the console login pops up (not the Xwindows login) and then the screen keeps on refreshing not allowing me to start Xwindows or login. Cntrl+Alt+Del works which just reboots the machine. Because I have lot of stuff already on the hard drive, I can't reinstall Linux because it would format the drive.
You need to boot the machine into single user mode but typeing at the lilo prompt LILO boot: linux single This will eventually get you to a BASH# prompt where you need to use a text editor to edit the /etc/inittab file. Change the number 5 to number 3 in the line id:5:initdefault: This will allow the system to reboot without trying to run the X login. Then rerun Xconfigurator to set the monitor to correct specifications. If you feel everything is again set correctly then you can change the 3 back to a 5 and reboot the machine.