My server has been running FC4 with all updates. After my son just accidentally unplugged it, it rebooted so that noone can login. If booted in text (mode 3), then after the login and password it just returns to login prompt. It can't be booted in single user mode. When this is tried, it says "going into single user mode", but then starts all the same services as mode 3 (AFAICT) and acts just the same. I booted into rescue mode, did chroot /mnt/sysimage, and looked at /var/log/messages and /var/log/secure. Nothing intersting shown. I can't ssh in. It just logs in and out immediately. Perhaps related, I had selected to disable selinux IIRC and it said it would relabel on next boot. Of course, it crashed before that happened.