I had the same problem of the screen flickering black on boot after updating Windows 8. The steps below use what I had available(2 networked PCs). You could do this using several others methods. I was able to solve this by doing two main things:
1. Copy the three theme files(themeui.dll, UXInit.dll and uxtheme.dll) from another Windows 8 machine's windows\system32 folder.
1a. I did this by using pstools(
psexec \\machine cmd.exe) on another machine to remote shell into the machine then cd to windows\system32 then rename those three files to .old like
move themeui.dll themeui.dll.old. I used command because windows was giving me permission warnings and such.
1b. Copy the new theme files to the machine using
\\machinename\c$\windows\system32.
2. Connect to the network registry of the machine to change the default theme back to Aero.msstyles.
2a. Start -> Run -> type regedit. File -> Connect to network registry. Input remote machine and connect to load the hive.
3. Search for key
ThemeManager and make sure your values for DllName are set back to default(%SystemRoot%\resources\themes\Aero\Aero.msstyles). I had one key set to the a theme at location HKEY_USERS\S-1-5-18\Software\Microsoft\Windows\CurrentVersion\ThemeManager. I looked under HK_LocalMachine and All Users at the location \Software\Microsoft\Windows\CurrentVersion\ThemeManager to verify they were all default as different themes change it at different places.