I am too having similar issues and here is everything I have tried.
First did a fresh install of windows 8 and then made a drive image using Norton ghost - everything working fine so far.
2 days later the kb and mouse no longer work at log in so I have no choice but to restore the image. Now everything works. Install a few apps and a few days later the problem comes back again. This time around I restored the image and added safe mode to
the boot options so on start up every time I an choose normal mode or safe mode.
woke this morning and pc worked fine. Come back from work, turn pc on and problem returned. Now I think ha! I have safe mode.... er no, keyboard and mouse don't work to allow me go select it and so after 10 seconds it boots to normal windows.
what ever the issue is it seems to disable the kb and mouse before OS select and it seems to happen (to me anyway) after approx. 3 days of using the pc.
pc specs
2x Samsung 250gb 830 series ssd
intel i7 2500k
16gb ram
asus P8Z68-V LX motherboard
MSI GTX670 2GB PE OC graphics catd