Macpro distorted lines freeze on boot

I have an 2006 macpro, nvidia 8800gt, yesterday my mac froze during diagnostics by onyx, there were green and pink wavy lines on screen, i did a hard shut down then trying rebooting, but immediately i see green vertical distorted lines and the boot doesn't get past by the apple logo. it freezes and have to shut it down.
i've tried:
resetting pram, smc
removing half the ram and then the other half
installed a new hdd, didn't really matter the same
i even removed all hdd, the same
can't start from os x dvd drive, freezes,
the same for safe mode
it does enter verbose mode, still the same lines, but i can't read all the commands, it's like it's half towards the left and other half is at the far right, but only the first letter of the commands, it's like i have a second screen.



now 2 weeks ago, i had a similar problem but my mac didn't even boot.
i replaced my graphics card and it worked fine, but just for a week, then again the same wavy lines during mac os x environment

any ideas?
I'm desperate

Try swapping the graphics card again to see what happens. If the graphics card swap doesn't help, you may be looking at logic board problems.

Maybe someone else who is better familiar with the Mac Pro line than I am can chime in and offer advice.

Open the Mac Pro up and make sure the 8800GT is properly seated and connected to the power take off on the logic board as you have changed the cards from reading your thread, and that should have resolved a graphics card problem.

After that logic board problems.

I'd also try a different monitor. In making changes, keep in mind the things that have remained the same. You didn't mention swapping out the display, so let's rule that out as well.