How did you install the video drivers?
Did you use Envy?
If no... try reinstalling them using Envy.
It's important to get the latest version
From his siteFor 1.7 you want Envy,
Not Envyng.
If you have bandwidth, run the Upgrade (not update) before you install your drivers.
Some people had driver issues that were resolved with the Upgrade.
After the upgrade completes, remember to install your drivers with envy before you reboot,
or you will get a black screen.