I think what you're saying is that the BIOS sees the HDD but the installation of Win7 doesn't? Is the HDD formatted in any different filesystem (a linux one for example?) You could try downloading the seagate HDD diagnostics, see if it picks up any errors, if not - try formatting it with the seagate diagnostics.
Updating BIOS and trying different SATA ports in the board is always worth a shot, but I don't think its going to really help you in this case.