Ah, the joys of being an early adopter...
Many people on this forum and also an Intel forum (I keep getting random hangs on Core...: Intel Communities) have complained about the onboard video of various Asrock boards (Pro3-M and Extreme4, at least). My first Extreme4 board had problems with both the HDMI and DVI connections; VGA/D-Sub worked fine. I'm on my second board and have already experienced a number of freezes using the onboard HDMI (DVI seems ok for now). I am currently re-testing my memory (just to be sure that nothing is wrong there) and once that is done, I will test the HDMI, DisplayPort and VGA connections again.
I would suggest you test with DVI and VGA and maybe DisplayPort. Also, make sure that your BIOS is up to date (check the Asrock site) as they recently released (on 7/11) a new version which ups the default voltage for the IGP. You might also check to see that your memory sticks are well seated and run memtest (or the like) for an extended period of time.
It may be a problem with the Z68 chipset or the Intel HD3000 drivers or with Asrock motherboards. I have not seen many people reporting this sort of problem with other motherboards and, unfortunately, I am loosing confidence in Asrock. If this board isn't rock solid then I will be moving on to one of the competitors; maybe dropping "down" to a P67 and discrete PCI-e video card.
I note that Asrock has posted 4 BIOS *upgrades* for both the Pro3-M and the Extreme4 on their website in just the last 2 months. Maybe this is an indication of teething problems with the Z68.