Appearantly this is related to the latest Dell driver. I figured out a workaround but it is a bit complicated: 1. Attach a USB drive that is large enough 2. Install Wndows 8.1 onto the *USB drive* 3. Boot into Windows, then remove the current driver, and install the previous driver for Windows Server 2012. 4. Use 3rd party software (say, Ghost) to copy the Windows from USB drive to VD on Dell PERC H710P controller. 5. Boot into Windows in USB drive again, and use "bcdedit" to clean up the booting stuff Anyways, I am getting LSI 9361-8i so this won't be an issue for me in the future...
My Dell PERC H710P (with latest FW A04) was working completely fine with driver 5.2.220.64 on Windows 8, until recently I tried out installing Windows 8.1 RTM on the machine, it caused FW hang when launching the Windows Setup: I believe Windows 8.1 was shipped with driver version 6.801.5.0 downloadable from Dell, which I have also tried and incurred the same FW hang issue. I am scared - does anyone know what is happening?? Cheers Chris 
Dell PERC H710P: Firmware hangs on Windows 8.1 RTM with default driver