Artifacting and display problems

I have been having many problems with (possibly) my graphics card artifacting and not displaying picture properly. Originally, my tower (very big) was sitting on some table and had artifacting problems on rare occasions. Now, I have it sitting on the ground (not much of a choice right now). Every time I stomp on the ground or step on ground too hard, the screen artifacts. One side of the screen will flip flop with the other, pixels may be jittery and misaligned, etc. Sometimes it may artifact if the GPU fan is running too high. If I unplug the HDMI cable and plug it back in, it corrects itself. However, this is starting to become a nuisance.

When I plug HDMI into the integrated Intel, there are no artifacting issues, although there is a noticeable decrease in computer performance. If I put my computer into safe mode while using my graphics card, it never artifacts. I find this really strange.

I tried many troubleshooting steps including plugging the graphics card into another PCI port, trying different cables, updating the driver, reseating graphics card, etc, all to no avail.

So I think that my graphics card is starting to bite the dust. However, it never has problems when running in safe mode. Is there a big chance that my graphics card is actually dying? Are there any other tests or troubleshooting steps I should try to run before deciding to buy a new graphics card?

I've had this computer and its components since around July 2011.

Intel i5-2500k Overclock 4.3 Ghz (water cooled)

SAPPHIRE Radeon HD 6850 1GB 256-bit GDDR5 PCI Express 2.1 x16

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