[Windows 8 High Start up times]

Hey if your Windows 8 is too slow and need to high start up times, you can try to use Windows Boot Genius.

[Windows 8 App just displaying blank screen]

Sounds like you might need to do a fresh install. I just had to do one last night on my laptop because of a DNS issue in Win8. Refresh and Reset didn't seem to solve it, so I had no choice. That's why his is a beta though.

Could try using the Repair options available on the Windows 8 disk (click Repair your Computer, instead of Install) before resorting to wiping it out completely though.

Good luck!