Few months before when I was using Ubuntu 12.04 then I found some errors while starting my computer.

Due to this problem I had given my CPU to a shop to repair it I don't know what he has done to my CPU but I only know that finally I got my CPU with Ubuntu 13.04.

The technician was unable to make any partition and I also think that he had installed 13.04 over 12.04 and so now my computer is showing some error when I'm starting my computer the error is as follows:

error: attempt to read or write outside of the disk 'hd0'.

grub rescue > _

Before showing this error, few times my computer was working very slow.

So kindly someone tell me that is there any way by which I can start my computer.

Please also tell me that what things I have to keep in mind while using Ubuntu so that in future I find no difficulties(errors) while using Ubuntu.