Make sure you are running one of the newer AMD drivers (AMD card, right?)
You might be having "handshake" issues where the HDMI signal is getting lost temporarily and screws things up.
Are you using both a monitor and a TV at the same time? If so are you doing all the switching at the AVR? There might be some adjustments you can make with your AVR, depending on how new it is. Seems I had to fine tune my Onkyo.
Use straight HDMI to HDMI if you can, and not DVI or VGA, although DVI to HDMI is probably OK.