Really need help with Crash Issue

Hello, I'm looking for help with a computer issue I'm having. I'm a modder of a game called The Elder Scrolls IV: Oblivion, and I've recently hit a snag in mod development. Recently my computer has been crashing over and over when I play the game. Now I know the first reaction would be to post this on the Oblivion forums, but for some reason I think the problem is not with the game, but my hardware. I haven't had too much issues with crashing the game lately, I have an old but good setup:

XFX 780i Motherboard, 8800 GT 512 MB, 4GB G Skill 800MHz RAM, E6850 Dual Core Intel Processor... It's been a good girl to me over the years and I love her very much. Recently I've been having some weird hiccups and slowdowns in certain things(the power supply died recently and I replaced it), but overall it's stayed a great PC. Recently though while testing some Oblivion mods I've been crashing.

I only crash when I move around too much. The Memory on the game shoots up to about 1.5-1.7 MB usage in Task Manager, and then after a few seconds of waiting in the wilderness my game will crash to desktop. This made me believe it was the game. But in one instance I got a CTD popup box, but the game continued to play so I alt tabbed over and kept on playing it. Eventually I got a new error: "0x8902382(or some other set of numbers) address in memory could not be read". I pressed OK for that error and then Oblivion crashed.

In another more recent instance, I was testing something in the wilderness again with no hitches for quite some time. Then I talked to an NPC and my screen went totally blank, the music froze for a second and the system hung in a black screen, then the music continued but my screen stayed black for a while. Very weird. But this is what leads me to believe its hardware related. Another reason is because once I start playing Oblivion a fan in my case immediately starts to make weird sounds...(I think its the Graphics Card).

The thing that makes me think it MIGHT not be my Graphics Card or hardware is because I can still play Dead Space in 1080p on my PC flawlessly, but I disable all of my mods and everything else in Oblivion and it just crashes over and over and over.

Other weird issues are:

- My card has no temps, no fan speed rating, nothing inside of ATITool except the clocks. All of them read "0".
- Sometimes my PC plays back videos super slowly, especially 1080p videos on Youtube(which is new)
- Sometimes my PC hangs while playing some Youtube videos (solved this by disabling hardware acceleration).
- Weird lag in some browsers.
- Had a hard time installing the graphics card drivers recently, lots of weird errors.

The current PSU I'm using is this: http://www.newegg.com/Product/Product.aspx?Item=N82E168... in case it might be my Power Supply causing the issues...I'm just at my wits end about this.

Both buying new hardware and reinstalling the game are difficult for me, so I want to try to figure out exactly what I need to do first before I do it...so if anyone can give me some guidance I'd appreciate it a lot.