Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
This means that your kernel looks for its root partition on in a place where there is none.
At a quick glance there are two possibilities as to what happened :
1)Your partition died; thus you kernel can't mount it.
2)Your menu.lst/lilo.conf got modified, and the kernel tries to read the wrong partition.
Are you using LILO or GRUB? If its GRUB, press "e" when given the choice to boot, and modify the "root=/dev/**** " section accordingly to your partition table (**** being the device and partition on which root is. e.g. /dev/sda2).
Else, you can download any LiveCD (knoppix for example), try mounting the partition, and modifying menu.lst/lilo.conf accordingly.
If you need more help, post menu.lst/lilo.conf here, as well as your partition table.
(don't write the *)