I have a problem that it looks like yours.

I have a ECS Desknote A900, and switching back to text console or
exiting XFree86, all I see is a mess. But I'm using XFree86 4.2.1 and
the 'sis' driver.

On Sun, 7 Mar 2004 17:46:33 +0000 (UTC)
tron@NetBSD.org (Matthias Scheler) wrote:

> 	Hello,
> 
> switching back to a text console with XFree86 4.4.0 gives me a black
> screen on my NetBSD-i386 1.6ZK system. I wonder if that's a general
> bug or specific for the ATI Radeon driver. Does anybody else observe
> this? If you do on what kind of hardware?
> 
> 	Kind regards
> 
> -- 
> Matthias Scheler                                 
> http://scheler.de/~matthias/