Video card problem with Mac Pro

Hello,
I currently have a MacPro down. It is a 2x2, 8 GHz, "Early 2008". 4 GB of memory. 10.5 and 10.6 installed. The video card is a Geforce 8800 GT (512MB). So for several days, the MacPro Planted: freeze total. I thought it crashed when I asked for the video card, like when I was playing a video game. And then to reboot, he began to plant too: Mac boots, gray screen with the apple, and then wham, freeze on the wheel lugs before displaying the desktop. Since then, he most boats, and always freeze at this point. Well, I tried everything. Reset the PRAM, repairing permissions, Apple Hardware Test (result: no problems detected). I also tried to change the internal HDD (I 3). The problem persists regardless of the SD which I boot. I also turned ALL the internal HDD, and started on the DVD system, even cares. Therefore, I was leaning towards a breakdown of the video card, since the problem seems to lie at the desktop display. Now I see on another post, there would be failures on these Macs, at the "module" of the hard drive. A breakdown of video card generates, does this kind of symptom, or else it must go to other causes? Thank you in advance for your expert advice?

Even I did had the same issue, but since I removed the internal drives (physically removed from the machine!),freeze and still with the DVD system, I do not think the trouble comes from there. I really look for a video card trouble, but how do you know? I would rather avoid the box "repairer", which begins with cost 200 $ before you even open the machine.

I would have taken the Apple Care anyway, I paid $ 2800 machine, and screen. I find the Apple Care and then, well, a machine "pro" is supposed to run for a while anyway. Especially since I always had plenty of Macs, no worries. Even my 400 MHz Titanium PowerBook still works very well, and the iMac G5 also (I'm on there). My use and the reason for my purchase is the pro audio. I sound editor. I work on ProTools. I also use it daily to the house, Photoshop, mail, internet etc. Thank you for your help.

I wanted to find a video card by myself, like in MacWay to avoid paying too much for Apple. After a few minutes searching on the iPhone (the WiFi Store), I changed my mind and I finally took an ATI Radeon 4870 directly to the store as they had in stock. I climb upon my return home, without worries, and the MacPro is left. Really hats off to the team AppleStore. What other store would have supported a Sunday, by appointment on a Monday, and part in stock solution in time?

Stretch your mac pro , get up in the cables, wait a minute, reconnect the cables following: video / power / mouse / keyboard, start your mac pro, but do not loose the button within 15 seconds, normally everything will be back in order. I also use a few lines of terminal but I do nothing on my Mac, especially this-that if I am wrong.

In fact, of course, I tried the 10.6.3 combo. So I installed. I have not seen significant change. But hey, no serious, in fact, the card works quite well, except for Doom 3, I do not know why the performance is below the 8800. But no worries with Bioshock, or X-plane which is even more fluid. But anyway, I did not buy this MacPro to play, but rather for the sound (as I mentioned above). Just that I do not understand why I had not even made in Doom, so I have a newer card.