This is my first time using Kubuntu for almost a month, switching from Windows. Somehow, when I install Kubuntu, it keeps being deleted by itself... when I forced to shut down the computer because of screen freeze or just shutting down normally.

This is my eighth time doing this. I don't know where all of my saved documents at the moment when Kubuntu keeps deleting by itself.

Any help please?

What do you mean by deleting?
What happens when you reboot the computer?

Kubuntu will not just delete itself. What do you mean; do you have a dual-boot machine or do you run Kubuntu from a CD?

Several times I forced the computer to shut down because of a screen freeze, and the other times are when I shut it down normally.

When I turn on my computer (or force restart my computer) it says something like "you need to have a CD to operate an OS, insert a CD and press any key". And I already installed Kubuntu several times.

Sorry, I'm just in a panic mode right now.

No, I don't have dual-booting

how do you reinstall Kubuntu?

I'm using Kubuntu via LiveCD at the moment. I had been installing Kubuntu several times "normally" when it gets mysteriously deleted. I don't know if it is the hardware problem or not.

After installing you should be able to remove the cd and boot in to the installation on your hard drive.

try typing the following and post the results
$ sudo -su
# parted
(parted) p all
you should see somthing like this

Can you elaborate, please? I'm still trying to learn how to use the terminal.

It also says that I "have 430.6 GB out of 456.7 GB (6%used)" on a 500 GB hard disk.

Where is the other 43.3 GB? I'm still not used to how Linux works overall though.

just type what your see excluding the "$" or "#" one line at a time.
If you do it incorrectly or the command is not install the system will tell you.
if you need more information on a command most commands will tell you how to use them if you type "man" and then the command. like this

remember not to type the "$"
The "$" just means your a normal user.
if you see a "#" your running as root.
sudo allows you to run commands as root.
using the live cd you dont know your password but they let you become root by just typing "sudo su". Then you can run commads as root(the super user).

as to the 43.3 GB i can tell you if you post the output of the commands as requested.

What i'm trying to find out is whether or not you have a linux partition on your hard drive if so you may be able to fix the system by reinstalling the boot loader grub/lilo. you may even be able to access your files from the live cd.

I typed "sudo su" instead and it worked. I followed the rest of your terminal guide and got:

Disk /dev/sda: 500GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number Start End Size Type File system Flags
1 32.3kB 494GB 494GB primary ext3 boot
2 494GB 500GB 5799MB extended
5 494GB 500GB 5799MB logical linux-swap

you have a linux partition at /dev/sda1 and a swap partion at /dev/sda5.

You probably just need to reinstall the boot loader.
what distro are you using(ie. ubuntu, fadora, suse).

I found out that there was a problem with my power supply. I had a very outdated power supply that made a lot of mess. I switched the an updated power supply and my Kubuntu is running very fine than before.