Oddly enough if you blow your hd away and do a clean install then everything will be missing that you had before, I wonder why ?
Try these actions to get your pc working again.
1: Install Motherboard drivers, from the manufacturer.
2: Install Drivers for any cards, graphics, sound etc.
3: Try doing a backup of your data before you do this again.
Have the above methods worked? AMD's drivers can be a bit odd. I don't know which, but one of the recent ones are really buggy. Go some web searching and find out which AMD drivers aren't buggy.
Also, a Core i3 (whatever gen) with the 7770 is powerful enough for Windows 7. Perhaps reading the OP might have been useful.