Ok so here's the issue.

I had a PROBLEM with not all memory being recognized by the bios, only 256mb shown, but Windows' System information would show all 512mb.

Occasionally all the RAM would be recognized and useable, but after awhile it would revert to only 256mb again.

This situation was really impeding the performance of the system, so i decided to buy another 512mb stick, so i would always have at least 512mb available.

However this didn't solve the problem as i would hope, and despite me trying them in all slots and different combinations, only 256mb RAM will show up. Occasionally 1024mb will be available, and this total also shows up in system information, but it doesn't happen often.

Anyways, i'm wondering, what COULD be causing this? I've run memtest for long periods of time and no problems are found with either stick, and i doubt it is a motherboard fault if the total does actually show up in system information.

Here's the best information i can find


Computer:
Operating System Microsoft Windows XP Professional
OS Service Pack Service Pack 2
DirectX 4.09.00.0904 (DirectX 9.0c)
Computer Name RICCOMP (Richard's Computer)
User Name Richard Tonge

Motherboard:
CPU Type AMD Athlon XP, 1666 MHz (12.5 x 133) 2000+
Motherboard Name Epox EP-8K9A2+ (6 PCI, 1 AGP, 3 DDR DIMM, Audio, LAN)
Motherboard Chipset VIA VT8377 Apollo KT400
System Memory 256 MB (PC3200 DDR SDRAM)
BIOS Type Award (11/08/04)
Communication Port Communications Port (COM1)
Communication Port Communications Port (COM2)
Communication Port Printer Port (LPT1)

Display:
VIDEO Adapter NVIDIA GeForce4 MX 440 (128 MB)
3D Accelerator nVIDIA GeForce4 MX 440

Multimedia:
Audio Adapter VIA AC'97 Enhanced Audio Controller

Storage:
IDE Controller VIA Bus Master IDE Controller
SCSI/RAID Controller SCSI/RAID HOST Controller
Floppy Drive Floppy disk drive
Disk Drive Maxtor 2B020H1 (20 GB, 5400 RPM, Ultra-ATA/100)
Disk Drive Maxtor 6Y060L0 (60 GB, 7200 RPM, Ultra-ATA/133)
Optical Drive IC2898R RMI711Z SCSI CdRom Device
Optical Drive LITE-ON DVD+RW LDW-401S (DVD:4x/4x/12x, CD:40x/24x/40x DVD+RW)
Optical Drive SAMSUNG DVD-ROM SD-616Q (16x/48x DVD-ROM)
SMART Hard Disks Status OK

and the RAM information:

[ DIMM1: AED660UD00-500C88N ]

Memory Module Properties:
Module Name AED660UD00-500C88N
Serial Number 0B1B2B9Ch
Manufacture Date Week 6 / 2007
Module Size 512 MB (2 ranks, 4 banks)
Module Type Unbuffered
Memory Type DDR SDRAM
Memory Speed PC3200 (200 MHz)
Module Width 64 bit
Module Voltage SSTL 2.5
Error Detection Method None
Refresh Rate Reduced (7.8 us), Self-Refresh

Memory Timings:
@ 200 MHz 3.0-3-3-8 (CL-RCD-RP-RAS)
@ 166 MHz 2.5-3-3-7 (CL-RCD-RP-RAS)
@ 133 MHz 2.0-2-2-6 (CL-RCD-RP-RAS)

Memory Module Features:
Early RAS# Precharge Supported
Auto-Precharge Not Supported
Precharge All Not Supported
Write1/Read Burst Not Supported
Buffered Address/Control Inputs Not Supported
Registered Address/Control Inputs Not Supported
On-Card PLL (Clock) Not Supported
Buffered DQMB Inputs Not Supported
Registered DQMB Inputs Not Supported
Differential Clock Input Supported
Redundant Row Address Not Supported

[ DIMM2: Kingston K ]

Memory Module Properties:
Module Name Kingston K
Serial Number 781FF861h
Manufacture Date Week 15 / 2006
Module Size 512 MB (1 rank, 4 banks)
Module Type Unbuffered
Memory Type DDR SDRAM
Memory Speed PC3200 (200 MHz)
Module Width 64 bit
Module Voltage SSTL 2.5
Error Detection Method None
Refresh Rate Reduced (7.8 us), Self-Refresh

Memory Timings:
@ 200 MHz 3.0-3-3-8 (CL-RCD-RP-RAS)
@ 166 MHz 2.5-3-3-7 (CL-RCD-RP-RAS)
@ 133 MHz 2.0-2-2-6 (CL-RCD-RP-RAS)

Memory Module Features:
Early RAS# Precharge Not Supported
Auto-Precharge Not Supported
Precharge All Not Supported
Write1/Read Burst Not Supported
Buffered Address/Control Inputs Not Supported
Registered Address/Control Inputs Not Supported
On-Card PLL (Clock) Not Supported
Buffered DQMB Inputs Not Supported
Registered DQMB Inputs Not Supported
Differential Clock Input Supported
Redundant Row Address Not Supported

Memory Module Manufacturer:
Company Name Kingston Technology Company, Inc.
Product Information http://www.kingston.com/products/default.asp

Thanks to all who can help.You either have bad or incompatable RAM. Put only one stick in and see what it shows. Run Memtest on it (www.memtest86.org for a free download). If there are no errors after an hour, remove it and put in another and do the same procedure. Then start adding two at a time and see the results, so you can pinpoint where the exact problem is. Write down your results and post them. We'll leave the light on.