Sudden decrease in performance, not sure why.

Hi PCMR,

I'm a pretty avid gamer, built my PC about 4 years ago and have slowly upgraded some parts. On Tuesday, I noticed that my CS GO was performing like garbage, my FPS was in between 20 and 30 and wouldn't go higher than 60 (barely ever reached 60). I also tried Hearthstone and noticed that the gameplay was choppy in ways I haven't experienced until now. The problem still exists today and after a bunch of researching and trial & error I'm still at square one..here are my specs:

• GPU: GeForce GTX 970
• CPU: Intel(R) Core(TM) i7 CPU 930 @ 2.80GHz
• Memory: 12.00 GB RAM (Corsair 4x3 ddr3)
• Motherboard: ASUS P6X58D Premium
• Current resolution: 1920x1080, 60hz
• Driver version: 364.72 (GeForce driver)
• Operating System: Microsoft Windows 7 Professional

In terms of settings, v-sync is off.

I've had the GTX 970 for about a year with no issues up until this point, so I'm inclined to believe it isn't my GPU (most recent driver update was weeks before this started). I recently upgraded my mouse about a week ago but I'm not sure if that would have any averse effects on my in game FPS. I tried a system restore in case something got installed that might have been holding it back but that didn't work, I also tried unparking the extra cores of my CPU but that doesn't seem to have worked either (I don't think the CPU is the problem either, it's performed well in conjunction with the 970 up until this point, not sure why it would suddenly be causing it to perform poorly)...any and all insight is greatly appreciated as I'm pretty much out of ideas as to where I could look/what I can try next.