256mb Xp is OK, 512MB system randomly reboots

Ok, I thought I knew everything (almost) until I ran into this bugger.
Here is what I have:
AMD XP1800
IWill XP333 board
64MB Nvidia Graphics card
2 256mb dimms from OCZ PC 2700 DDR
Windows XP Pro (NTFS)
Built this system for a friend. Everything ran fine from February to June. In June PC started acting up. Random reboots, graphics went to 640 X 480 at 4 bit, wouldn't always turn on, CMOS put CPU at defaults (1150MHZ at 100 Mhz).
He decides to tell me after a month of this happening.
So, I change CMOS to 133Mhz and CPU jumps back up to normal. I fix the video card problem by uninstalling driver and letting Windows reinstall. Got video at 32bit 1024 X 768.
At this point I am rocking and rolling. Then it reboots and reboots and reboots whenever it likes.
I take out a DIMM leaving one 256 module in. Using Sisoft Sandra 2002 I stress tested it for over 24 hours with no problems. Swapped the memory modules around stress tested for 24 hours and still no problem.
As soon as I add the second DIMM, I can get it to crash and reboot by running a cache/memory benchmark, or by just using the computer normally for awhile.
I have tried every DIMM slot combo. I have replace the power supply with a 430 watt.
I am thinking this is a hardware issue, but I am looking for any ideas. I will try 2 different DIMMS this evening.
This defies logic, but sometimes computers do. Maybe I am not thinking this through. Everything is fine with one DIMM in and in any DIMM slot. Put 2 in and random reboots consistently.
Any suggestions would be appreciated.
Tim

1. RE: 256mb Xp is OK, 512MB system randomly reboots
lbyard Aug-01-02 11:56 PM
In response to message 0

I went over to Iwill's site to check on one of the things I would suggest considering and that is flashing the BIOS. I couldn't find anything. I am very unimpressed with the tech support side of Iwill's site--abosolutely terrible. If you are more patient than I am, you might see if you can have more success than I did. Larry

2. RE: 256mb Xp is OK, 512MB system randomly reboots
timw88 Aug-02-02 00:29 AM
In response to message 1

LAST EDITED ON Aug-02-02 AT 00:31 AM (EDT) by lbyard (admin)

Already flashed to latest BIOS.
There site absolutely *****, but you never plan on needing it.
I am working on increasing VIO setting (voltage to the memory) and I am seeing some stability increases. But I am just not sure on why I have to do that at this point when it was running fine before.
Still looking for the answer, any more help is appreciated.

3. RE: 256mb Xp is OK, 512MB system randomly reboots
lbyard Aug-02-02 00:44 AM
In response to message 2

Try putting both memory modules in a different pair of slots. I don't know about mismatched DDR memory modules, but that is an occassional problem with older types of memory. Larry

4. RE: 256mb Xp is OK, 512MB system randomly reboots
Rod Aug-02-02 05:51 AM
In response to message 3

I would say it is definetly your memory causing this.
The best way to find this out would be get the memory and stick them in another pc and see what happens. I bet the same thing would happen in another pc with both of them in there.
Rod

5. RE: 256mb Xp is OK, 512MB system randomly reboots
timw88 Aug-03-02 00:02 AM
In response to message 4

I found an awesome FAQ from Mushkin on their website that has helped me greatly with this problem. I wanted to share it:
http://www.mushkin.com/cgi-bin/Mushkin.filereader?3d4b5254037a05a62741c0a8010205b8+EN/products/990587#four
My configuration of 2 256MB modules + Ali Magik chipset is what I believe caused the problem. According the faq some boards have stability problems running more than 1 module due to capacitance loads. Secondly, Ali magik chipsets can have problems addressing more than 256MB.
I finally got the system down to an acceptable stability level. I did this by adjust my voltage to memory jumper from 2.5v to 2.7v. I have also scaled back some bios setting to run the ram more stable.
Now I have only been able to crash the system once within the last 24 hours, and that's with throwing everything and the kitchen sink at it. Thanks for the input however.