Yes Fred... I also thought that the on-board graphics would be disabled automatically but it was not getting disabled in my case and thats what was causing Windows 8 Pro installation to fail and then driver conflict if I installed Windows 7. See this picture below -
I was able to solve this problem with the below tricks. -
1. I uninstalled all both Intel & AMD drivers with driver fusion in windows safe mode and shut down the pc.
2. Popped out i5 3570k from mobo and re-fitted it once again so as to negate any socket issues. Did CMOS reset. But this did not worked and the problem was reproduced.
3. Popped out i5 3570k and this time popped in a spare i3 2100 I had with me. Did CMOS reset and installed windows 8. It got installed perfectly. Then I tried installing Windows 7 and that also got installed perfectly.
4. Now I popped in i5 3570k again. Did CMOS reset and tried to install Windows 8 Pro. And yes this time all worked perfectly. I now could install all the drivers and stuff.
5. PC is running stable now
Luckily I had a spare LGA1155 proccy lying around me... this would not be everybody's case. I really wonder how the above trick worked. Can you please throw any light on this going by your technical expertise ?
It would be great for my knowledge if you could explain to me the mechanism by which motherboard would disable the on-board graphics. My understanding was that the Z77 chipset on my motherboard would have these instructions sets and not the motherboard itself.