Computer Issue Please Help

Hello

My computer issue is that my PC shut down on itself when 1/2 hour into any of my video games. Now it shutdown after 15min of web surfing. My video games are Dawn of War, Sin of a solar empire, homeworld 2, and Guild wars. I got the games in march and everything work but in middle of may this started. My PC is Gateway GM5084

My spec are
CPU:AMD athlon 64X2 4200+
RAM: 2GB
GPU: Nvidia Geforce 6100
OS: XP media center edition 2005
HD: 320GB
PSU: 350 watts

PCSoul

Thank for the software and you were right it is a temps. problem. My PC temp are

AMD Athlon 64 X2 4200+ hardware monitor

Temperature sensor 0 53°C (127°F)
Temperature sensor 1 56°C (132°F)

WDC WD3200BB-22KEA0 hardware monitorHDD

Temperature sensor 0 37°C (98°F)

ACPI hardware monitor

Temperature sensor 0 26°C (78°F)

ITE IT87 hardware monitor

Voltage sensor 0 1.34 Volts [0x54] (CPU VCORE)
Voltage sensor 1 1.17 Volts [0x49] (VIN1)
Voltage sensor 2 3.28 Volts [0xCD] (+3.3V)
Voltage sensor 3 5.05 Volts [0xBC] (+5V)
Voltage sensor 4 11.65 Volts [0xB6] (+12V)
Voltage sensor 5 -12.99 Volts [0xCB] (-12V)
Voltage sensor 6 -10.18 Volts [0x9F] (-5V)
Voltage sensor 7 4.95 Volts [0xB8] (+5V VCCH)
Voltage sensor 8 2.91 Volts [0xB6] (VBAT)
Temperature sensor 0 31°C (87°F) [0x1F] (TMPIN0)
Temperature sensor 1 43°C (109°F) [0x2B] (TMPIN1)
Temperature sensor 2 49°C (120°F) [0x31] (TMPIN2)
Fan sensor 0 2482 RPM [0x44] (FANIN0)