Common GRUB/LILO problem

If you install Linux (I’ve had this problem with Gentoo and Mandriva) and LILO gives you a weird error like L 01 01 01 01 01 ... and just hangs, and/or GRUB gives you Error 21 and just hangs, you can try the following:

• Check if your BIOS settings are correct — specifically if your hard disks are configured properly.

• Check if a non-graphical bootmenu works fine.

I had the first problem with Gentoo on one machine, and the second with Mandriva on another! And here’s what the GRUB manual says about Error 21:

21 : Selected disk does not exist
    This error is returned if the device part of a device- or full file name refers to a disk
    or BIOS device that is not present or not recognized by the BIOS in the system.