Are you talking about the Slackware distribution? The boot disks gave a clue but you should identify what distribution you are using in your questions.
If you are installing Slackware and if your computer will boot from the CD-ROM then use the CD based installation. The boot disk + root disk method uses very old kernels with very limited hardware support. You can find download mirrors at www.distrowatch.com
. Note that you only need the first two CDs to install Slackware with KDE. You only need the first CD to install Slackware without X software.
If, again you are installing Slackware, and if your computer will not boot from a CD-ROM then try a boot disk that has SCSI support. USB hard disks use the SCSI driver.