Installation of Service Pack 1 for Windows 7 fails with error code 0x800f0a12
This problem is mostly that other operation systems are installed, like GNU/Linux or BSD.
The solution is simple, Windows must to be installed on the first partion/harddisk in your system.
To make this possible simply open your computer (after shutdown) and remove the power-supply
from harddisks, there not contain your Windows installation.
Install the update and add the power-supply back to your disks.