distorted lines freeze on boot

[ninjawt]

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.

http://i54.tinypic.com/2q0ixar.jpg

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

 

[JediMeister]

Sorry to say, the only thing that all the steps you've taken wouldn't fix is a busted logic board. You already know it's not software, which a new HD/new OS would have fixed. If not memory/video card, you're running out of hardware components to isolate to.

 

[goMac]

Your GPU is dead. Common issue with the 8800. Likely the replacement is also dead. The replacements are not fixed cards.