I am not able to use the computer because my gives disk error when i start the computer , this is due to hard disk or due to something else.

Thanks

What the error says could help.
Often it a hard drive failure or corrupt operating system.
But could be many other things as well;
bad or loose hard drive cable
hard drive not set as boot device in BIOS

Try re-seating the cables, check that it's set as a boot device in the BIOS and run diagnostic software on the drive.
SysChat - Downloads (Freeware Utilities) - Ultimate Boot CD