If you opted to install LILO, instead of creating a boot floppy, then you should be able to boot Linux from the hard drive. However, the automated LILO installation procedure used by many distributions is not always perfect. It may make incorrect assumptions about your partition layout, in which case you will need to re-install LILO to get everything right. Installing LILO is covered in Chapter 4.
Another command to try (with MS-DOS 5.0 and higher) is
FDISK /MBR
This command will attempt to rebuild the hard drive master boot record for booting MS-DOS, overwriting LILO. If you no longer have MS-DOS on your hard drive, you'll need to boot Linux from floppy and attempt to install LILO later.
On the other hand, if you did install LILO, and another operating system boots instead of Linux, then you have LILO configured to boot that other operating system by default. While the system is booting, hold down or , and press at the boot prompt. This should present you with a list of possible operating systems to boot; select the appropriate option (usually just ``linux'') to boot Linux.
If you wish to select Linux as the default operating system to boot, you will need to re-install LILO. See Chapter 4.
It also may be possible that you attempted to install LILO, but the installation procedure failed in some way. See the previous item.