AMI doesn't update BIOS for boards used in Gateway PCs. THe 780 board is like beating a dead horse it is already doing everything it can do, The 785 is a much better choice so it will be a new board, memory and a processor. thanks
If you change the motherboard, I hope you have the "retail" version of Windows 7. In this case, you can uninstall Win 7 from the old motherboard and then change out the motherboard and do a fresh install on Win 7 on the new motherboard which would be like a new and different computer.
This is not possible to do with the OEM version of Win 7 which is motherboard and CPU specific, and technically not transferable to a different motherboard. In this case you will have to call Microsoft and explain your situation, and depending upon their discretion, they may activate the license. No guarantees.