you are saying here I believe that your Hard Disk is dead, but ... sometimes it shows that in my PC, then it works fine by itself ... crazy nah? Try to change the Sata cable that connects your Hard Disk to the Bios ... it might be of a bad quality ... If that won't solve it, try connecting it somewhere else.

Can you hear your hard disk working? If not it might be a power problem, the HD is not getting electricity ... To solve that, they have to change the Chip on the HD and you can do that by buying another similar HD, get the new chip and replace the old one.

You can also try to buy one of those HD enclosers that will convert your HD to a USB HD that you can connect just like any external HD.

So sorry to hear that and i hope that would help, but i never believed in Seagate as I know many people who faced many problems like that, or a part of the HD will get corrupted and go beyond repair.

Do not dwell in the past, do not dream of the future, concentrate the mind on the present moment. (Gautama Buddha)