I have the exact problem you have. At first I didn't have any sound from my HDMI so I downloaded the newest vidio drivers and not when I start up the picture is fine till i come to the dest top. Been trying everything. Anyone have an answer?
I haven't found anything, I've just been using the older drivers.
I emailed support but got no reply back. If you find anything, then post it here.
Similar problems here but I get a corupt picture on all my monitors. Each day when I first boot the Win7 Welcome/Logon screen looks fine. I type my password and the desktop shows up fine and then after about 1.5secs it screws up. Then I hit Win+L to go back to the Welcome screen and it looks fine. Then type my password and it messed up again. The only solution I have found is to reset the video drivers using devcon.
I used AutoHotkey to assing this command line to Ctrl+Win+Alt+V:
devcon restart =Display
You can download devcon.exe from here:
So now if the video gets all screwy I just hit the hotkey, then hit Win+L to get the logon screen and then type my pass and I am back to work. I have to do this every day now. It all started with 1986. I also have a 4500HD. I upgraded to the new driver to get Flash 10.1 beta to work.