Now first, please notice I am not an expert, I am still learning....
Aren't we all As you correctly point out this board has no onboard graphics but attempting to start it without a graphics card installed is unlikely to damage it. As the Extreme Series boards are aimed at enthusiasts and people who may want to extract every bit of performance from their hardware, it's likely that buyers will want to install high performance graphics cards which far outperform Intels onboard graphics.
If it's not booting and you've double checked all the connections according to the product guide from here: http://www.intel.com/p/en_US/support/highlights/dsktpboards/db-dx79si (have a good look at all the options accessible from there - you'll learn alot) since you are using a liquid CPU cooling arrangement, what is plugged into the CPU fan motherboard header pins? Some motherboards don't like running with no fan plugged into the CPU fan headers as a safety measure but the instructions for your cooler kit may cover this....
did you solve your problem?
If you turn on the board without an grafik card it normally would end in a beep mesage of the bios (2 beeps repeating all 2.5 sec).
If that dosnt happen bios may not even get to the step to check for the Grafic adapter.
Does the board turn on at all or does it stop after certain activity?