This is a problem with grub, your bootloader. It seems that grub cannot find its configuration file, so it is dumping you at a prompt where you can boot manually.
To boot manually, assuming your kernel is in a /boot partition on /dev/hda1 you would do this:
grub> root (hd0,0)
Filesystem type is ext2fs, partition type 0x83
grub> kernel (hd0,0)/mykernel root=/dev/hda2 vga=791
[Linux-bzImage, setup=0xa00, size=0x10b949]
Remember that grub prompt has tab completion, so if you don't remember your kernel name:
Possible files are: mykernel myotherkernel etc.....
You are also able to load an initrd using the same syntax...
I rather suspect though, you would prefer to fix grub so that you are presented with a nice menu instead. As mentioned, your problem generally means that grub can't find its conf file. The file is generally in /boot/grub, but on some systems it may be in /etc. The file itself is called grub.conf or possible menu.lst.
Check that this file does exist in the right place. You may need to reinstall grub so it can find the conf file. If you need help with this just ask. I also recommend doing this from a grub prompt rather than using the grub-install script.