Intel Mac :: Screen Flicker And Glitch On 24", Early 2009?

For a while now, my iMac has been having somewhat random display glitches, flickers, freezes, and kernel panics that can only be fixed by shutting down the computer. Most of these screen glitches go like this: The display flickers black quickly, letting me know that an issue is going to arise. The issues that could happen are as follows:A blue line glitch (very common)a random artifact glitch (somewhat uncommon)a freeze-up (very common) a kernel panic 

There are several types of "display glitches" I've been experiencing. Some of them involve random artifacts that are randomly displayed and seem to be hovering over whatever is going on on the screen–for example, once I was browsing Facebook and the glitch occurred, so a square of my browser screen was sort of cut out and stuck on the screen above everything else going on. The issue wasn't fixed until I restarted the computer. This glitch, however, wouldn't show up in screenshots. These are somewhat less common because it seems if this one happens then it either gets worse very fast and there are random pieces of my active windows all over the screen or it freezes the computer up entirely, or even results in a kernel panic. 

Another "display glitch" that is far more common is a sort of line glitch. It's very strange: blue lines will outline random shapes and things all over the screen. Pictures on my browser appear distorted and videos look VERY weird. The dock has the lines and random blue pixels as well. The desktop background appears distorted. This glitch often starts with the screen flickering black and the various blue lines appearing. The lines change shape as the objects on the screen move around.The issue doesn't appear in screenshots but I documented it by taking crude videos and pictures on my phone that give examples.

Here's a link to my video of a video about a nonrelated screen glitch. I was actually searching Google for a solution but it turned out to be unhelpful, but since the screen glitch happened to be going on I decided to record it as an example. Notice how the blue lines move with the video...

NOTE: My computer actually JUST screen glitched and froze up completely, at which point I had to shut it down and reboot. Luckily the post was saved! Just in case you were wondering how often these things occur.

This issue is getting worse and worse. I'm not sure what triggers it, but it seems like graphics-intensive programs like 3D games can trigger it–especially, it seems, when I toggle on and off fullscreen. It looks like it could be a graphics card issue, because if it was a software problem it would seem like it should show up in the screenshots. It's sort of an underwhelming graphics card, but meh. My mom is having a panic attack and backing up everything on the computer and we're thinking about just reinstalling OS X altogether.

Here's some general info about the computer:General info: Model Name: iMac  Model Identifier: iMac9,1 Processor Name: Intel Core 2 Duo Processor Speed: 2.93 GHz  Number of Processors: 1 Total Number of Cores: 2  L2 Cache: 6 MB Memory: 4 GB  Bus Speed: 1.07 GHz Graphics and Displays:Chipset Model:NVIDIA GeForce GT 120  Type:GPU  Bus:PCIe  PCIe Lane

[code]...

Info:
AppleTV 2, Mac OS X (10.7.3), 24-inch iMac, Early 2009