Nvidia GTX 770 in a Poweredge 2900

Hey guys,

I have a Poweredge 2900 with redundant 900w power supplies and currently running a modified Geforce 7800 graphics card (16x to 8x by cutting pins). The card that I would like to run is a GTX 770 which requires a ton more power (600w vs ~120w). I am upgrading because of a program I need to run requires a CUDA enabled card. I have tried a few things and am coming up a little bit empty handed. Keep in mind I'm actually a Geologist, so my terminology might not be spot on, so bare with me! My progress so far:

-Did the 16x to 8x modification (hacked off the 'extra' pins) on the GTX 770

-Tried to power it using sata power from empty HDD slots - came up with a 'HDD fault' on the two sata slots I tried to use...as if the plugs were read as failed hard drives. I considered this a failed attempt because I could not figure out how to disable this error for the computer to boot.

-ordered a 600w power supply (which is just sitting next to the computer - not hard mounted in any way, but its safe don't worry ;) ), bridged the switch. I was able to get the computer to boot to the bios screen, however it would not continue to boot windows (7). it was also only powering one of my two monitors.

Does anyone have any suggestions on where to go from here? I've heard some people suggesting that the on-board graphics card should be disabled before another one can be used...do you think this applies to me? is that possible? Also, in your responses if you could be as specific/descriptive as possible, I would really appreciate it (like I said I'm not an expert). 

Thanks!