Sudden poor performance in a decent computer (Win 7 64-bit)

Hello all, and thank you for reading. I will try to keep this brief, but I'll try and explain my situation as clearly as i can. Recently (Thurs/Fri) I began experiencing a sudden drop in performance in nearly every facet of using my computer. Mind you, its not a severe drop, but enough to make gaming and media experiences frustrating. A few examples: poor response on anything media related, in particular youtube, an extreme increase in load times on games such as League of Legends and Torchlight 2, and a very noticeable drop in framerate in said games, and also (for lack of a better description) a general lagginess when web browsing or otherwise using windows. Im relatively experienced with computers, but definitely not a pro. I did have one BSOD earlier in the week, but thought nothing of it as my computer had been on for at least a couple of days, though that isn't the norm for me. I have beat the internet up, down, and sideways for a solution in the past 48 hours, and frankly i dont know what else to do. Here's what i have done. Downloaded HWmonitor to check voltages and temps, downloaded HD tune to make sure my HDD is functioning properly and not trying to quit, downloaded and re downloaded several different Spyware programs to check for malicious activity which I ran in safe mode, scanned and rescanned with AVG to check for and malicious activity, opened my case and checked every single cable and port to ensure positive connections, unseated and reseated my GPU, ram, and graphics card to ensure positive connection, blew out and cleaned dust from the inside of my case, checked all fans to make sure theyre operational, and even ran /scannow in an admin cmd prompt. In the process of trying these different options I used League of Legends as a benchmark, as I reliably get 60 FPS through an entire game, regardless of graphics strain. Lo and behold, when I tried to run it this morning, I get a game crash in between loadscreens. Rather, the game just doesnt load. I tried to use Starcraft 2 instead, and run into the same issue as it tries to update. Whether this is important or not i have no idea. I have steam and AVG running in the backround, nothing else. Ive kept a close eye on my task manager processes to see if I could find a memory hog. After i finish writing this, im going to set Memtest running and get some sleep. If anyone has any ideas/tip/tricks/witchcraft, insight would be wonderful. Thank you for your time, and apologies for the wall of text.

hey all, sorry it took so long to get back. yes i tried reinstalling my graphics drivers several times, but i never actually uninstalled them completely and then reinstalled, so ill try that.