Please Help! AMD FX-8320 FPS Bog Down/Drops/Chops Randomly

My computer isn't running games smoothly, it's got a high FPS rate in games but will randomly drop FPS hard and sometimes also freeze entirely

So, this is my first time ever posting on a forum about tech advice, as I just bought my new computer 2 or 3 months ago and it's my first foray into the world of PC gaming, so you'll have to forgive me for being an idiot.
My problem is that when I'm playing games, for example Metro 2033: Redux or DayZ Standalone, I get a steady FPS [I use nVidia ShadowPlay to see my FPS] but when I'm playing, seemingly randomly, my FPS will drop either to half, a third, or just freeze the game entirely, usually for a second or two up to 15 seconds or so. I didn't have this problem, I don't think, for games like Far Cry 3 when I first got my comptuer, and that's somewhat graphically demanding also. My computer specs are:

AMD FX-8320 3.5 GHz
nVidia GeForce GTX 650 1GB
8 GB of DDR3 RAM, unknown type but I'm sure it's 1600 mhz
500w Bronze Certified power supply

It's a pre-built gaming computer I bought from NewEgg, an iBUYPOWER PC or some such, and I realize the parts aren't that fantastic, but I should still have enough oomph to boss Metro and DayZ at a stable rate at least, even if I have to turn settings down to medium or low. When I set everything on Medium on Metro Redux I get 70-90 frames, which will randomly drop, which is most noticeable when things happen on the screen, or when I turn to look at something, it's like my computer bogs down when it's processing/rendering to put things on my screen, which it shouldn't, because it should be way more than enough to handle it. I've tried using all settings, disabling all settings, running everything at Very Low, same problem, nothing helps. I know DayZ Standalone has optimization issues, but I shouldn't have my computer freeze entirely for 15 seconds when I'm playing, for any reason whatsoever. I've checked some forums and threads that reference my CPU or GPU but I have seen nothing really about my specific problems. I don't know anything about overclocking or how to do it, only roughly what it does [speeding up your CPU/pushing it to maximum performance while sucking more juice/running hotter I think?] but I'm almost certain I won't have to go near that stuff to just run games I bought and play them how they were meant to be played, at a steady framerate. I know enough to know that even with my stock build, without messing with anything, I should be able to play something on low-to-medium settings and have it run SMOOTHLY, not bog down no matter what I do. I'm currently getting CCleaner to try and clean my registry like I've seen in some other threads, but I really need advice or preferably a solution on how to fix this problem. I don't really care if it's lengthy or complicated, I'm sure I can figure it out once I know what it is I need to do, but I'd prefer options that don't require spending money, at least not much, because I shouldn't have to to make my computer work the way it's supposed to.

Please please someone help me figure this out!