Oz, these modern Asus boards come with lots of features, some of them may be causing this confusion.
The error message, "no hard disk detected" may be coming from the IDE controller. If you are using all SATA drives, there is nothing attached to the IDE controller so it flashes up that message. That's also why it would go by quickly. If it sat there a long time, it would slow down the boot process.
This motherboard also has ExpressGate, which is the much hyped feature that lets you boot a small Linux environment directly from the motherboard. Since this is a Linux kernel, it might be what is putting up the GRUB message. It would be best to disable ExpressGate in the BIOS for now.
You should go through the all of the BIOS settings and check them. Consult the motherboard for any features you are not familiar with. Also, did you check for and apply a BIOS update?