I believe my graphic card has just gone out

I have a 2008 Mac Pro Tower and (I believe) the graphic card has just gone out. I can still access the tower remotely (via home sharing for Apple TV, etc) but the direct monitor is showing a crazy squiggle pattern (usually about five minutes after the machine initially boots). I've checked, and it's not an issue with the monitor itself.

If this alone was the issue, I'd feel 99.9% sure I could replace the video card.

But in addition to the video issue (during those five minutes before the video goes out) the Mac Pro is having random 10 second mini freezes where the mouse or an application launch suddenly stops.

I'm hoping this mini freezing problem is ALSO related to the graphics card issue. I'd hate to spend the money on the card only to learn that it doesn't still resolve half the problem.

Can anyone say whether video card issues could also cause the processor to have clunk issues?

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