It could happen that your system hangs during boot up. If so, do not panic, just keep reading.
If your system hangs during Rebuilding RPM database or Finding module dependencies, just press Ctrl-C. This will allow the system to skip this step and continue to boot. Once booted, execute rpm --rebuilddb as root if the hang was at the Rebuilding RPM database phase. If the hang was at the Finding module dependencies phase you have most likely been through a kernel upgrade, but have not done it properly. Check if the files in /boot and the /lib/modules directory match the current kernel version (i.e., have the current version number attached). If they do not match, please read Compiling And Installing New Kernels from Reference Guide to find out how to fix this.
If the boot process hangs at RAMDISK: Compressed image found at block 0 you have messed up the initrd image. Either try to boot another lilo.conf entry or boot an emergency system and remove or change the initrd= section in /etc/lilo.conf
If, for any reason, you have not shutdown your box properly, the system will run a routine file system check during the next boot. It may sometimes fail to do this on its own and will drop you on a console. Execute e2fsck -py [device] where [device] is the name of the partition on which the automatic check has failed. The -p switch tells e2fsck to do all the necessary repairs without asking, -y assumes the answer yes to all questions. When the check and repair phase is over, press Ctrl-D to leave the emergency console. The system will reboot.
If you get this error regularly, there might be bad blocks on your disk. Execute e2fsck -c [device] to find out. This command will automatically mark any bad blocks and thus prevent the file system from storing data in these blocks. e2fsck checks the file system automatically only if it has not been unmounted properly during the previous system shutdown; or if the maximal mount count has been reached. To force a check, use the -f option.