Mac pro 3,1 8 core, hangs at bootup, at the same spot

Thanks Grant
forgot to mention i had two pair of ram sticks(both of which work fine with no lights at any time other than that flash at startup), and ive tried each pair invidually. All fans are spinning.
I think the key somehow to all this, is how exactly i can replicate the behavior. every single time i boot it locks up in the same exact place, at the same exact time. the mouse never moves from the upper left hand corner. The keyboard never gets to type anything or even turn the caps lock light on. I checked with a volt meter and power is getting to the usb port . but things like pressing option or shift at start up do not appear to be working (which means that i have probably not suceeded in reseting the pram. I also dont hear a startup chime.
the screen more or less looks like this (althought i have a different name, picture ect) http://i.i.com.com/cnwk.1d/i/tim/2012/07/05/BlackLoginWindowMask.png

Tommarow im going to try to make a ubuntu install usb stick, and see if i can use that to learn more, or even get this freaking thing to boot

dang, i didnt even realize that, i just thought that was the background image. The screen im at has my name, picture and password field with a cancel button at the bottem but my regular background image in the back, with no graphics artifacts at all. Just to be sure ive already tried with two different gpus.
Thanks though Grant

https://www.dropbox.com/s/hxmknv0281qelbj/2012-08-13%2017.55.42.mov
heres a video of my issue including a my screen at the hang in lion , sorry about the file size, but at least you get some good detail on the screen.
I have been unable to get to safe mode in any OS, it seems like its not taking any of the normal pre-bootup keyboard shortcuts like option, shift, verberose and so on or even go into the recovery disk mode. I dont have an original disk for this thing sadly so i havent been able to try that. interestingly enough, sometimes after hanging i do hear some HDD activity for a few seconds after, and then after that i do hear an occational seek every 30 seconds or so.

Thanks again for your help Grant

yes that box with blue text is from my display. and i knew i was forgetting something in that last post but yes ive tried 2 different keyboards each plugged directly into the mac pro case, on both the front and back :/ I tried just holding shift, repeatably hitting it, waiting till when i think the startup tone should have gone off (but never dose) then holding down shift .

no, no, and no :/

took out all the hdds, the ssd and the optical drives, it only gose to the regular folder with a "?" not a menu. I tried each disk indivdually, no good :/

yes, it means if i want to swich boot disks, i literally have to remove all the drivers except the one i want to boot from. just made a brand new lion boot disk using the ultility and it gets past the spinning gear, flashesblack, and then solid gray, and thats it 😟
Tried taking out one of the ram cards(not dimms) out, and held the debug light button, which is in the ram cage, the standby light was soild the whole time, and the gpu efi and whatever the other one were all green as they came online, the erra and errb lights never came on, nore did the sleep light.
Its too late tonight but tommarow im going to make a ubuntu dvd and try to boot from that :/