I've had this when i used the DVD install image with 710b4 and a Nvidia 6600Gt APG card
i went round in circles as it looked like a possable bad system ram/heat issue. Found info on the web todo with the nvidia agp settings (google for nvagp issues)
In the end i did a full reload with the CD install method.
Works a treat now.
What hardware you using,
What install method you using etc......