Games keeps crashing?

When i play games after about 10-30mins the screen will freeze and not turn back on, forcing me to restart the computer. Windows 7 can find no soulution when restarted. Games ive tried where this happens is World of Warcraft, Counterstrike and Bioshock.

Computer Specs:
OS Name Microsoft Windows 7 Home Premium
Version 6.1.7600 Build 7600
Other OS Description Not Available
OS Manufacturer Microsoft Corporation
System Name ALIENWARE-PC
System Manufacturer To Be Filled By O.E.M.
System Model To Be Filled By O.E.M.
System Type X86-based PC
Processor Intel(R) Pentium(R) 4 CPU 3.40GHz, 3398 Mhz, 1 Core(s), 2 Logical Processor(s)
BIOS Version/Date American Megatrends Inc. 1019.004, 26/10/2004
SMBIOS Version 2.3
Windows Directory C:\Windows
System Directory C:\Windows\system32
Boot Device \Device\HarddiskVolume1
Locale United Kingdom
Hardware Abstraction Layer Version = "6.1.7600.16385"
User Name AlienWare-PC\AlienWare
Time Zone GMT Daylight Time
Installed Physical Memory (RAM) 2.00 GB
Total Physical Memory 2.00 GB
Available Physical Memory 1.26 GB
Total Virtual Memory 4.00 GB
Available Virtual Memory 2.84 GB
Page File Space 2.00 GB
Page File C:\pagefile.sys

Card name: NVIDIA GeForce 6800 GT
Manufacturer: NVIDIA
Chip type: GeForce 6800 GT
DAC type: Integrated RAMDAC
Device Key: Enum\PCI\VEN_10DE&DEV_0045&SUBSYS_00000000&REV_A1
Display Memory: 743 MB
Dedicated Memory: 248 MB
Shared Memory: 495 MB
Current Mode: 1440 x 900 (32 bit) (60Hz)
Monitor Name: Generic PnP Monitor
Monitor Model: JLM1901SG
Monitor Id: JSY0001
Native Mode: 1440 x 900(p) (59.887Hz)
Output Type: HD15
Driver Name: nvd3dum.dll
Driver File Version: 8.17.0011.9713 (English)
Driver Version: 8.17.11.9713
DDI Version: 9Ex
Driver Model: WDDM 1.0
Driver Attributes: Final Retail
Driver Date/Size: 3/16/2010 07:51:59, 9386088 bytes
If you need anything else posted let me know, please help thank you