ATI Radeon 4870 x2 HELP!

im having a problem with my 4870. every time i try to play a game higher than the low settings it crashes my computer. i can play the games higher as long as they're in windowed mode like crysis i can play full spec in windowed as soon as i go full screen it crashes. here's what i got:

-MSI 790FX-GD70 AM3 AMD 790FX ATX AMD Motherboard
-VisionTek 900250 Radeon HD 4870 X2 2GB 512-bit
-Antec TruePower New TP-750 Blue 750W Continuous Power ATX12V V2.3 / EPS12V V2.91 SLI Certified CrossFire Ready 80 PLUS BRONZE
-AMD Phenom II X4 955 Black Edition Deneb 3.2GHz Socket AM3 125W
-G.SKILL Perfect Storm 6GB (3 x 2GB) 240-Pin DDR3 SDRAM DDR3 2133 (PC3 17066)
-Western Digital Caviar Black WD1001FALS 1TB 7200 RPM SATA 3.0Gb/s 3.5"
-Logitech G19 Black USB Wired Standard Gaming Keyboard
-ASUS VW266H Black 25.5" 2ms(GTG) HDMI Widescreen LCD Monitor
-Microsoft Windows Vista Ultimate SP1 64-bit
-XIGMATEK Dark Knight-S1283V 120mm Long Life Bearing CPU Cooler

all of this is in an Antec 1200 case. and one problem i have with the memory is that it wont fit in my dimm 1 slot due to the massive heatsink for my CPU.

its 6 gigs but its clocked at 1333 i havent overclocked yet cause i dont wanna void any warrenties till its fixed.

no i havent flashed the BIOS

I'm using the adm drivers all up to date

i have not changed the clock speed but i did change the 3d settings

1920x1200

my biggest concern is when it was first installed there was a small whisp of smoke so i'm currently getting a replacement but iv had other systems that did that but work just fine. it was just a peice of dust ignigting or something. and if i flash the bios i have to reinstall windows right?