hello

Firstly, I'll give a sequence that lead to desaster

1. Installed X distro which came with grub
2. Changed my mind that I want slack, in order to do so I then try to remove grub. Unfortunatly due to my carelessness, I issued a wrong command dd if=/dev/zero of=/dev/hda bs=512 which subsequencly wipe out ,what I beleave to be ,the primary partition or the boot sector (I'm not sure). But that is alright since I'm going to install Slack anyway.
3. Managed to installed slackware10.2 from CD from start to finish, with error free. Before the installation, I delete and recreate all the needed partitions with fdisk. That went by ok as well.
4. On first reboot, now here's the problem, my comp can't find the harddisk.
5. Booting from Slack CD1 bypassing a command to boot from harddisk result in a kernel spit out half a page of error messages related to disk error and freezed.

I hope the damage is not permanent, if there's a recovery procedury, I would be so glad to know. Thanks

You could troubleshoot this problem for awhile, but in my opinion I would take the fast approach: fdisk and re-install
You have nothing to loose, since you already "flattened" the root partition. On the other hand if you have data in your home directory you may want to boot with a "live CD" get your data and then start all over.

Hope this helps.

But before I installed Slack, I've fdisked to delete everything and recreating all the new partitions already. Or is it possible I missed something?

Well ... to me you have a problem with the boot loader. But unless you are familiar with Slack and linux it is faster to re-install.
If you feel courageous you can troubleshoot and re-install the boot loader.
BTW, I assume that when you say you mean that the system cannot find the boot sector and therefore it fails to boot. Or you mean that your computer complaints that there is not HDD ?

it complains that there is no bootable CDrom in the drive - this, I suspect that the system had skipped the attempt from booting from hdd to looked for CDrom booting instead, as specified by the booting sequence in the BIOS. Therefore I beleave the system can't "see" the harddisk.

Get an up-to-date liveCD - Knoppix should do.
Redo the fdisk from there to ensure it writes the partition table and disk signature bytes correctly. Used to be a problem, but I used a Knoppix 3.9 CD to succesfully rebuilt a disk I deliberately trashed like you did (as a test a couple of months ago).

Just an idea: maybe you installed lilo to the root partition. In your case it needs to be installed to the MBR. In lilo.conf you should have
or whatever your harddisk is. You can fix this by booting off your slackware CD, and then passing some parameters to lilo when you run it (forgot what they are).

Yeah, you're right, it was the misconfigured LILO. I booted up with Slack CD1, chrooted into the drive to make the change. No need for reinstall. Despite having experience with GNU/linux for some time, I tend to freak out with simple problem like this, that I can't help posting. Now it is cured.