Help me troubleshoot another flaky ECS K7S5A based system

[TangleWeb]

System description;

• ECS K7S5A Pro v5.0 motherboard.
• AMD Athlon XP 1800+ (1.53 GHz) running at defaults.
• 512mb RAM = 2 x Simpletech PC 133 (UD256133N38K11091703)
• 20 GB Maxtor 32049H2
• SONY CD-RW CRX215E1
• Nine Visual Technologies Revolution 4 32mb AGP
• Allied PSU Model AL-A300ATX Rev:B in inexpensive, but decent quality mid-tower case.

Symptoms & troubleshooting;

• Owner said that in the midst of doing something routine in Windows the system spontaneously rebooted. When it came back up the BIOS settings were set to defaults, no drives detected, etc. Of course it didn’t boot into Windows which is when I got the system.
• When I benched the system, I re-configured the BIOS, hitting F3 to re-detect all drives & booted into Windows without a problem. I installed SiSoft Sandra & ran the included Burn-In utility overnight (over 10 hours) without a problem.
• In case the BIOS was the issue (I have seen this many times on ECS boards), I flashed the BIOS to the latest ECS provided BIOS dated 08/11/03.
• I also replaced the CR2032 CMOS backup battery with a new one for good measure.
• Now the weird thing – I booted to a Memtest-86 CD & it ran for less than a minute then locked up. No errors were displayed on the Memtest-86 screen, it just “froze” with a flashing cursor at the bottom left of the screen by (ESC)EXIT. When I re-booted the system, the BIOS was re-set to defaults. This happened consistently, every time I re-configured the BIOS & booted to the Memtest-86 CD.
• I pulled the two Simpletech sticks & installed a random 64mb stick of PC 133 SDRam I had laying around & Memtest-86 has run 8 passes on it for 45 minutes so far without error, or freezing.

Background;

• System was custom built 10/30/03 (By me)
• I got the system back 08/10/04 as it was completely infested with spyware. I performed a clean install of the OS & apps at that time. I also ran Memtest-86 & noted numerous errors, so replaced the 1 x 128mb & 1x 256mb PC 133SDRam with the above mentioned Simpletech 256mb sticks of PC133. I ran Memtest-86 on these to verify that they were good & they were.
• Now here it is July 3, 2005 & the RAM seems to be bad again.

Is it possible this setup is killing RAM? Is there something else going on here?

This board supports both SDRam & PC2100 DDR RAM, so I'm going to install a couple of sticks of PC2100 DDR RAM & see if I fare better with it.

~Dave