but i am able to run battlefield 3 at around 30-40 fps in medium-low settings. But why not tf2

Ok so starting from a couple of months ago my TF2 started getting really bad frame drops from like 120 to 5-10 in middle of fights. I have a fairly new computer. I don't really know much about computers so i really need some help fixing this.

my computer specs are

cpu: i7 - 3770
gpu: amd readeon hd 7470 2 gb
ram: 8 gb

I belive that's all you need

Also i tried Chris's highframes, maxframes and dx9 configs but they didn't help much

so this is my first time playing competitive and i would like someone to teach me some strategies and stuff for this upcoming season. I know the roll outs and stuff, its just that i don't really know what i'm supposed to do in certain situations like in mid or last. I would really appreciate if someone would help me.

my steam id: http://steamcommunity.com/profiles/76561198034281170

Thanks in advance :)

wait, can anyone actually join and play without being pro :(