I too. I have the same video card (ATI Mobility Radeon HD 5470 ( HD 5000 series) and same error.
I bought windows 8 64 bits (pro) and I'm very happy with it.
It boots much faster. Everything works better comparing to win 7.
I downloaded and installed the 13.8 beta drivers (amd site)
(amd_catalyst_13.8_mobility_beta.exe)
All ok.
The driver is accepted and the fans are less noisy.
No conflict in device manager.
But when I (re)boot the pc I see a black screen now.
The only thing what helps is clicking once shortly on the power button.
Then another time.
Then I see the normal login screen.
Can you please help me to resolve this black screen, I'm so happy that the drivers are working within win8.