How to restore my disk

[Dennis Cao]

Yesterday, I used this command to correct my MBR on my working computer,
    $ dd if=/somefile of=/dev/sda  bs=512 count=1
But very unfortunately, I used a wrong file. Now when I boot my
working computer, it says:
   Non-system disk or disk error
   replace and strike any key when ready

I think the partition table is destroyed. How can I restore my disk?

---------------------------------
曹贵林 ( Dennis Cao )