Do I have problems with my card?

So I overclocked my XFX 8800gt alpha dog edition to around 700/1700/1900, which from what I've read is quite modest. I am using stock cooling though, just turned up really high. However, I downloaded CoD4 off of steam and it's starting to freeze a lot after a while, it just freezes and stops responding, and the screen may turn a different shade of color, one time white snowy stuff seemed to cover the image, which I guess is artifacting? However, I ran a lot of stability tests afterwards, and no problems came up. During testing temperatures can go up to 80 degrees, but while I'm playing cod, the temperature pretty much never goes above 70. I'm using 3dmark as well as the fur rendering program. Is this a problem with the card, or is it a problem with cod on steam? I'm not really sure.

Oh I see, is installing an aftermarket cooler hard? I'm still kind of learning the ropes. the fan is already set at 95% because at 100 it instantly gets a lot louder for some reason.

Also, this is kind of an unrelated question about fans- I have an intake fan in the front, a fan in the back, a fan in my psu that moves a lottt of air, and a side fan, its front-in, back-out, which i guess is pretty obvious, but what should i do with the side fan? it came blowing in, but doesn't that defeat the purpose of the cpu fan if the hot air can't get out?

Yeah, that makes sense, but is one better than the other?

ok, thanks for the tips =)