Help! Computer that has frequent random errors (BSOD)

Help! my computer has frequent random BSODs. Sometimes its 0x0000050, bad pool header, 7E, 8E, 1A, 1, IRQL not or less equal etc.. When BSODs happen, it will restart then I will restart windows normally; sometimes it will be successful, sometimes not. But errors are not always the same, and they happen very randomly and I do not know how to repeat those errors again. Before, I ran memtest and it said there were errors with memory. i tried putting the ram in the second slot (before in DIMMA1, now DIMMB1) and rerun memtest. It now determined no errors with the memory. But still I get BSODs at times. I do not know now what to replace (GPU or memory or cpu or the motherboard itself??) here's the specs:

OS Name Microsoft Windows 7 Ultimate
Version 6.1.7600 Build 7600
Other OS Description Not Available
OS Manufacturer Microsoft Corporation
System Name CHUAFAMILY
System Manufacturer VIAK8M
System Model AWRDACPI
System Type X86-based PC
Processor AMD Athlon(tm) 64 X2 Dual Core Processor 3600+, 1900 Mhz, 2 Core(s), 2 Logical Processor(s)
BIOS Version/Date ACRSYS - 42302e31, )Phoenix - Award WorkstationBIOS v6.00PG, oC(Phoenix - Award WorkstationBIOS v6.00PG, 12/29/2006
Windows Directory C:\Windows
System Directory C:\Windows\system32
Boot Device \Device\HarddiskVolume1
Locale United States
Hardware Abstraction Layer Version = "6.1.7600.16385"
User Name ChuaFamily\StephenRamosChua
Time Zone Taipei Standard Time
Installed Physical Memory (RAM) Not Available
Total Physical Memory 2.00 GB
Available Physical Memory 763 MB
Total Virtual Memory 4.00 GB
Available Virtual Memory 2.72 GB
Page File Space 2.00 GB
Page File C:\pagefile.sys

Thanks in advanced for your help...