I am guessing here because you don't tell us about your computer or OS. My guess
is that you have Ubuntu 8.04 because this an Ubuntu group and your computer is 5
months old, which is too old for version 8.10. Is this correct?

The OS is likely intact provided that you did not destroy it with the disk you
got. You probably don't need to re-install if this is the case because Ubuntu is
very durable and forgiving of crashes, etc. Please let us know more so that we
can help.

What do you see on the screen? What happens when you don't put in the disk? What
happens when you put in the disk? What error messages do you see, if any? Tell
us anything that may be of use about your computer, such as the number of drives
or partitions. I ask this because sometimes there is a recovery console
installed on a second drive or partition and you press a Function key to get
into it. It will be in your documentation.

The biggest problem that I could see from what you say is that you may have done
something with the disk to erase your original installation and there is no OS
on your hard drive which is why it does not work with the disk.I am not sure
what the instructions were or what you did, so this is all speculation. Best
case scenario is that it is all there, but it is not booting due to an error of
some kind.