need help in running fsck to try to fix Linux hard drive

Greetings.

I have a Debian Linux box that will not boot -- hangs after giving copyright notice on egrep .... anyway, I've booted the computer from my Knoppix CD and I can see all the files, so perhaps there's hope....

I was thinking of trying to run fsck to try to fix the problem ... does that make sense? if so, should i

umount /dev/hda2

or umount /mnt/hda2

before fsck /dev/hda2 ....

i'm SO confused ... anyone who can help me do this -- or provide alternative suggestions -- i'd really appreciate it.

boot the knoppix cd/dvd with:
knoppix nofstab noswap

This will prevent knoppix from scanning the HD and will minimize access attempts.
Then try the fsck:
fsck /dev/hda2