All PC games suffering from massive framerate issues. Requesting help.

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I have been getting persistent FPS issues in pretty much all of the games on my PC. I first noticed it when playing Counter-Strike: Global Offensive, and then experienced it again in Team Fortress 2. Both games have experienced a recent drop in performance within the last two days: yesterday it was CS:GO, and today, as of about 30 minutes ago, TF2 has encountered it as well.

It strikes me as particularly odd because one minute I'm playing the games and all is fine and dandy with the world. Then the next minute, smoothness goes to hell, aiming is near impossible, and the games become generally unplayable. What's more is that both games suffered from the FPS drops at different times, making it hard to say whether or not it's a hardware problem.

I went in to Red Faction: Guerrilla to test and see if the problem wasn't solely Source Engine-related. It was MUCH worse there, as the FPS in the menu went into the single digits, and there were even missing textures.

To further my investigation, I played Just Cause 2 which is not connected to Steam. Likewise, JC2 was unplayable, so it's not just a Steam-related problem either.

I don't, however, have any problems with games that don't require 3D rendering (i.e. The Binding of Isaac, Intrusion 2, etc.). This makes me wonder if it's a GPU problem. I jumped in Minecraft and found that there were pink lines everywhere, a problem I've had in the past. Changing a setting in my NVidia control panel solved that problem, so I suppose it's possible that something's been changed for the worse on my GPU, but I'm not sure what it is.

I have a Nvidia Geforce GTX 550Ti. Any and all help would be appreciated. Thanks.

*Edit: I've done a bit more testing with GPU-Z and discovered that whenever I'm playing a game like JC2, the GPU load is 99%, so it's being taxed hard. Probably has something to do with it.

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*Fixed. It was a driver problem. Silly me.