Disabling all partition recognition except /
 

My hda6 partition where FC4 is messed up. Whenever I boot into FC3 (hda2), it gets hung up because there are errors on hda6 that cannot be fixed and stops the bootup of FC3. I used linux-rescue and was able to mount hda2 and edit /etc/fstab and commented out hda6. However, hda6 is still being seen at bootup.

How can I fix or disable hda6 so that hda2 can boot?

I'm not sure you can, short of deleting the partition itself (which will delete all of your data - Do Not Do That). The bootloader is doing a scan of all the partitions on the disk, not just the ones that /etc/fstab tells it that it will need.

If even fsck doesn't fix the errors I'd have to recommend getting yourself a new hard drive fairly soon, before that one quits out completely...

I was able to fix hda2 with fsck and boot into FC3. I used a live cd
(Slax) and umounted the harddrives. Then I checked each partition:

fsck /dev/hda1
fsck /dev/hda5
fsck /dev/hdb1
fsck /dev/hda2

This last one I had to do manually because it had a lot of errors and
could not be automated (-a)....it took about a half hour.

FC3 will boot now. I'm still without half my drive (hda6). I tried
re-installing FC4 but it doesn't see hda6. How can I reclaim hda6?

When you run `cfdisk /dev/hda` (as root) does it show hda6 as a valid partition?

I rebooted a live cd and issued cfdisk /dev/hda to see the partition table and it was read correctly...hda6 is seen as a Linux partition. hda6 is where a new install of FC4 resides and has the default partition type (I'm not sure exactly what type-it just says Linux partition whereas hda2 says ext3 for FC3).

Also, fsck gives this error on hda6:

[root@LinuxHippy linuxhippy]# fsck /dev/hda6
fsck 1.36 (05-Feb-2005)
e2fsck 1.36 (05-Feb-2005)
fsck.ext3: Attempt to read block from filesystem resulted in short read while tr ying to open /dev/hda6
Could this be a zero-length partition?

EDIT:

Here's the cfdisk /dev/hda output:

Name Flags Part Type FS Type Label Size (MB)
-------------------------------------------------------------------------------------------------
hda1 Boot Primary Linux ext3 /boot 104.77
hda2 Primary Linux ext3 / 9941.05
hda3 Primary Linux swap 536.74
hda5 Logical Linux ext3 /email 209.54
hda6 Logical Linux 9733.06

That's usually indicative of a bad block on your physical hard drive, which isn't in any sort of software's power to fix.
If you know the block number (usually spit out by fsck when it finds the bad block), you can try to manually black it out so that the hard drive doesn't have fits when it sees it anymore.
See this forum post for more detailed information. I stand by my earlier comment, though: back up anything else on that hard drive that you care about as soon as you can, before the whole thing, and not just a couple of sectors, takes a nosedive.

It's actually the first 13 blocks (0 to 12). Do drives usually have 1 block at a time go bad when the whole thing is bad? Maybe I got a boot virus (I did have MBR problems that I had to first fix)?

Oh, and what about Low Level Format-would it fix the bad blocks? My drive is a Western Digital that came with LLF software. I realize I will lose my data in the process, so I have a 2nd drive (a Fujitsu) that I can back it onto first.

Formatting it should either fix the bad blocks, or at least block them out so they're not used at all. Warning, though - this might not be a permanent fix. It'll take care of the bad blocks that are evident now, but it can't fix the ones which might potentially show up later.

I'm going to guess that it wasn't a boot virus. It pretty much sounds like the drive is slowly quitting, and is finding it harder to retain data correctly.
And it's not so much that a drive goes bad one sequential block at a time, as simply that it starts going bad...and you can't really tell when it's going to quit out altogether. Sort of like wearing a hole in your jeans...one day it's just a couple of rough threads, which if you tug too hard while putting them on you'll end up with a nice big rip across the knee :-)

Looks like you were right-it was the harddrive. I backed it up tonight and then tried the Western Digital LLF (Doc Cal) and then reinstalled FC4 and started getting weird file errors after the install. Then I wiped it again and installed FC3 with the same result. Guess I'll be pulling that drive tomorrow. Not sure if I should buy a new 80 GB harddrive or put in my old 4 GB harddrive (I already have a 6 GB drive installed). My pc is 6 years old and I'm wondering what else could go wrong with it...plus I just upgraded the CPU and installed a DVD player.