Strange Low FPS When Gaming

Hey there, first of all lemme start off by apologizing for any mistakes I may make, this is my first time posting on a tech site.

The Situation

I've had this computer for perhaps five years now and have been a frequent user (about everyday, mostly gaming.) I've had my share of issues, but never something quite like this.

Recently when playing any of my games, they will run fine as normal, but then will suddenly drop to incredibly low rates of FPS for about a minute or so before returning to normal for another minute and returning to the laggy state.

At first I had thought it may have been my internet connection to these games, so I attempted to play an offline game on Steam with the same effect. So I attempted a game loaded from my disc drive (Dragon Age Origins) and was given an error I've never seen before "The program can't start because PhysXLoader.dll is missing..." I also tried Guild Wars 2 but with the same FPS problems as every other game.

So I thought the missing .dll was my issue and attempted to download Nvidia's PysX installer, but the installer wouldn't even attempt to install and I could find no solution as to why.

So, in an attempt to find another solution, I ran my games with Windows Task Manager up and was monitoring to see what was taking up the most memory when these drops in FPS occurred. I found that Steam was the highest running program, so I tried closing Steam and playing Guild Wars 2 to no avail.

I also tried cleaning my PC of all dust, installing the newest driver for my Nvidia card, and running all these games on their lowest settings with no solution.

I'm starting to think that it isn't actually a software issue but is in fact hardware and that my GPU is starting to kick the bucket.

System Summary

OS Name Microsoft Windows 7 Home Premium
Version 6.1.7601 Service Pack 1 Build 7601
Other OS Description Not Available
OS Manufacturer Microsoft Corporation
System Manufacturer MICRO-STAR INTERNATIONAL CO.,LTD
System Model MS-7529
System Type x64-based PC
Processor Intel(R) Core(TM)2 Quad CPU Q8200 @ 2.33GHz, 2336 Mhz, 4 Core(s), 4 Logical Processor(s)
BIOS Version/Date American Megatrends Inc. V2.4, 3/26/2009
SMBIOS Version 2.5
Windows Directory C:\Windows
System Directory C:\Windows\system32
Boot Device \Device\HarddiskVolume1
Hardware Abstraction Layer Version = "6.1.7601.17514"
Installed Physical Memory (RAM) 4.00 GB
Total Physical Memory 4.00 GB
Available Physical Memory 2.15 GB
Total Virtual Memory 8.00 GB
Available Virtual Memory 5.63 GB
Page File Space 4.00 GB
Page File C:\pagefile.sys

Forgot my GPU - NVIDIA GeForce 9500 GT driver version 9.18.13.1422

I'd be happy to respond with more information if more is required. Any help would be appreciated before I start considering buying a new GPU.