If it's still the ASUS M3N78 Pro, then this board is almost 5 years old, and doesn't appear to have any Windows 8 specific drivers yet. Also, it doesn't look like the BIOS has been updated recently, but make sure you have the most recent which is 1402 (from 2010)
For a board that old, I would stick with the Windows device drivers for the motherboard and chipsets, since it's likely that those drivers are newer than the ones on the Asus site.
306.97 is the latest WHQL driver, so that should be good.
Are you overclocking? If so, you might want to go back to default speeds for a while and see if that helps.
Check your bios settings for the power management and sleep settings, and play with those.
Try disabling Fast Startup
http://www.eightforums.com/tutorials/6320-fast-startup-turn-off-windows-8-a.html
Did you do an upgrade install over Windows 7? Or did you do a clean install? You may have to do a clean install if you cannot solve the problem.