Seagate internal disk not getting detected

You can go to disk management and initialize the hard drive.

Right click on computer and select manage , then select disk management and in the window that pops up you can see all the drives that are connected to your computer and if it already doesn't show a window on your screen to initialize the hard drive you can rigtht click on the Seagate drive and select initialize or create new partition and follow the instructions.

After disk management > Check BIOS to see if it shows up there, if not, you have a drive failure.

Quite agree with inzone. I would suggest the same tip above for you.

If it is lost due to virus, software error, then you may need to restore files from it at first.

Does the drive spin up? If not, then it is probably a PCB issue, in which case a straight board swap should work.

http://www.donordrives.com/blog/pcbswapguide
http://www.donordrives.com/hard-drive-pcb-donor-swap-ma...

What is the model number?