I have downloaded an ISO file of Ubuntu 12.10 x86 from the official website (www.ubuntu.com). When I tried to install it, everything was going good until I got the error message something like
The media you are using is probably corrupt or you have a hard disk error. It did't tell me what to do.
I'm already running Windows 7 Ultimate on my PC and it's running fine. I have tested my hard disk for error and no errors were found by System Mechanic Pro 11. After that, I tried to install my Windows 7 on the same partition and it was successful.
Even now I am unable to install Ubuntu.