Hey.
You can't just take a hard drive from another computer and expect it to load the OS on another. There are all sorts of drivers specialized for each system. It is not technically impossible for the OS to boot well after lots of it "fixing" itself, but this is very much a no-no in every sense of the word. Whenever there is a new motherboard, you can never use the "old" OS. Clean install is absolutely needed. Again, it's not technically impossible...just very much should never be attempted or done for various reasons.
I would low level format the drive you intend to install Windows 7 to with Killdisk and then proceed to install. Good luck and enjoy.
In the Asus bios, make sure Plug and Play OS is set to yes. Many installs go foul on Asus machines because this is not set well.