Pc STILL blackscreening in more graphically demanding games

Have you checked the GPU temps while gaming?

Also, what brand and model is your GPU?

the model is an nvidia EVGA geforce gtx 570 1.5gb
the highest temp ive seen it reach playing borderlands 2, or skyrim(the 2 games that it happens the most in) is about 80c

That's damn hot. Hot enough for it to be a problem. That's likely your problem.

so how do i fix it? ive already had the card RMA'd. theres no dust in the fan. what do you suggest?

start with the mb bios. make sure it up to date. use cpu-z make sure the ram running at it rated speed and timing.look at the spd tab. make sure in the bios achi mode is on and ram running at xmp profile. check that the ram and cpu running at At a 1:1 ratio. download msi afterburner make sure the gpu fan turns on 100 percent at 50-70c temp.

80 degrees is a little warm, but nothing to worry about as a max (not average) temp.

What PSU are you using?

im using a corsair 750w (62v?) psu

80c is not hot for a GPU. Many will run close to or over 100c. The s/ware will try control the fan for 80 under load. Noise vs Heat.
CPU's run cooler tho. They usually restart completely, no hanging etc.

Sounds like it's the motherboard if you have replaced everything else.

To diagnose the problem you really need another system in spare parts. Then swap one component out at a time till you isolate the problem.

HAVE FUN!!!!!
/sarcasm.

Say what you want about Mac's, but I switched our 2 businesses over ~4 years ago and to date our 13 devices have had zero h/ware failures or issues (touch wood).
Running PC's before, i once replace 2 systems' PSU's in one week. I also had a PC test bed out the back to swap components in and out. It gets useless as slots and sockets are upgraded over time.
It can be fun to mess around with your own system, but I'm not in IT, I've got real work to do  
Only reason I joined Toms years ago was to diagnose shop built systems that were always giving dramas.

well, ive tested another graphics card, using a gts 240? and it didnt seem to happen(granted, its not very capable of running those games these days) does that say anything?

shut down windows auto updates. disable auto driver updates ( 2 different things ) uninstall nvidia drivers, reboot. install nvidia drivers but do a custom or advance install. when prompted only install the graphics driver and physx drivers. nothing else. what happens?

ive already tried that. nothing different.

MB is a possibility. the x58's were really bad for a while.

the "new" card isn't new. it's just a replacement.

try a very early driver (nvivia).

have you updated the mobo drivers at all since new?

no raid functions enabled in BIOS?