Help Random Crashes and Restarts System Not Stable

Question

im having stability issues in my new system...especially when running 3d games most of the time random restarts and crashes.....this is my system specs
Msi Neo 875P
P4 1.8 533 northwood
256 kingston pc2100
256 k-byte pc2100
(both rams on A channel 2.5v setting)
Ati9800 pro
120 gig wd 7200 RPM
60 gig WD 7200 RPM
(both on ide 1)
DVD Rom
DVD burner
(both on ide 2)
Ata controller
120 gig seagate 7200
120 gig seagate 7200
Hercules 5.1 Sound card
Thermaltake Case
400watts PSU
using windows XP SP1 fresh install..using the latest ati drivers...bios is stock and ram settings set to auto ...the voltage is set to 2.5 and dynamic overclocking is disabled... performance set to slow...using single channel on memory....they say its the memory thats having the problem having 2 diff brands??or the motherboard is picky when it comes to memory modules??i cant use ddr400 coz it requires 800mhz FSB and that will cost me more buying a new processor.....the airflow in the case is working fine...i hope you guys can help me thank you very much!!!

Answer 1

this is my power supply and some information about it
P4ATX-400W Dual Fan
Switching Power
AC INPUT: 115/230 Vac~ 14/7A 60/50Hz
DC OUTPUT :                                                                                                      
COLOR BROWN RED WHITE YELLOW BLUE PURPLE BLACK GREEN ORANGE
DC +3.3V +5V -5V 12V -12V +5V-SB COM PS-ON PW-OK
OUTPUT 20A 40A 0.5A 17A 1.0A 2.0A RETURN REMOTE P.G.
+3.3V and +5V max Output 240W, Peak Surge Max Output 436W
Features
High efficiency
Low Ripple & Noise
Output over voltage protection
Short circuit protection on all outputs
Reset table power shut down
Approved by UL, TUV, CB & CE
INTERNAL 12 VDE fan
Complies with FCC part 15 subpart J Class B at 115VAC operation & CISPR 22 Class B at 230 VAC operation
100% burn-in under high ambient temperature(50¢J)
Vacuum-impregnated transformer
MTBF:100K hours at 25¢J
100% Hi-pot tested
FULL RANGE 100~240VAC
Input Characteristics
Voltage: 95-132 VAC or 180-264 VAC switch able
Frequency: 47 Hz TO 63 Hz
Input current: 10 amps maximum/ 115 Vrms,60 Hz. 5 amps maximum /230 Vrms,50Hz.
Specification
Remote ON/OFF Control: The power supply shall accept a logic collector level which will disable / enable all output voltage (excluding +5V standby).
Temperature range: operating 0¢J~50¢J, storage -20¢J ~ +80¢J
Temperature coefficient: 0.01% / ¢J
Transient response: output voltage recovers in less than 1 ms max. following a 25% load change
Hold-up time: 16ms minimum at full load & nominal input voltage
Dielectric withstand: input / output 1800 VAC for 1 second, input to frame ground 1800VAC for 1 second
Humidity: 5~95% RH
Efficiency: 65% min. 70% typical, at full load
Power good signal: turn-on delay 100 ms to 500 ms
Overload protection: 150% max.
Inrush current: 60A cold , 80A ware at 132 VAC
Over voltage protection: +5V output : 6.5V; +3.3V output: 4.6V;+12V output: 15.5V