PC crashes when playing games on Asus Striker II Extreme, need help please.

Hello everyone, not sure if this is the right place to ask for help, but hope i can learn something here.

I have just finished building my new gaming pc for the first time, but its really unstable, every time i play games, the game will crash after roughly 5 mins and exit to windows with a messenge saying XXX.exe has stop working, or sometimes when i try to download something or have it turned on for longer than 2 hours i get a blue screen. I dont have any experience with pc building before, therefore i have not the slightest idea on what might be causing the problem. I hope some of you here could give me some advices.

My PC has the following components

CPU: Intel e8400@stock speed
MB: Ausu Striker II Extreme (I haven't watercool it, i just leave the fusion block with rubber caps on)
Memory: 8gb ocz PC3-10666C7 1333MHz ddr3 (4x2gb)
GPUs: BFG GTX 280 in sli
HDD: Samsung 1TB SATA
PSU: Tagan BZ 1300
OS: Windows Vista Ultimate 64bit

I have ran real temp and cpuz and got a screen shot in the attachment, the temp for my cpu is 32C at idle and 39C at load for both cores according to real temp, but everest is showing 42C at idle and 50C at load, i dont know which one is more accurate, and here is the information everest is showing

Field Value
Sensor Properties
Sensor Type IT8718F + W83791D + ADP3228 (ISA 290h, SMB 2Dh, SMB 20h)
GPU Sensor Type Driver (NV-DRV)
Motherboard Name Asus Striker II Extreme / Formula / NSE
Chassis Intrusion Detected No

Temperatures
Motherboard 37 °C (99 °F)
CPU 25 °C (77 °F)
CPU #1 / Core #1 42 °C (108 °F)
CPU #1 / Core #2 42 °C (108 °F)
MCP 61 °C (142 °F)
GPU1: GPU 73 °C (163 °F)
GPU1: GPU Ambient 49 °C (120 °F)
GPU2: GPU 57 °C (135 °F)
GPU2: GPU Ambient 47 °C (117 °F)
Temperature #2 -47 °C (-53 °F)

Cooling Fans
CPU 2848 RPM
Chassis 1160 RPM
Chassis #1 1160 RPM
Chassis #2 1400 RPM
Chassis #3 1412 RPM
Fan #1 737 RPM
Fan #3 1197 RPM

Voltage Values
CPU Core 1.26 V
+3.3 V 3.33 V
+5 V 4.97 V
+12 V [ TRIAL VERSION ]
+5 V Standby 5.08 V
VBAT Battery 3.23 V
CPU VTT 1.12 V
CPU PLL 1.52 V
North Bridge Core 1.33 V
South Bridge Core 1.52 V
HyperTransport 1.33 V
DIMM 1.81 V
DIMM VTT 0.90 V

Please if anyone has any ideas or opinions about this problem, please let me know, i will be very appreciate.

Thanks.