I have 2 sticks of GSkill PC3200 RAM (Timings: 2.5-3-3-6) . I've verified both sticks work properly on other systems when running at 200 MHz.
However, when installed in the ASRock 939Dual-SATA2 and manually set to 200MHz, the system becomes extremely unstable (memtest fails, and numerous operating systems fail to boot -- at one point, the computer even failed to reach POST and I was left staring at a black screen). Additionally, if I try to use the two sticks (which are identical) in dual-channel mode, I run into the same issues.
All of my RAM settings in the BIOS (version: 2.30), other than the frequency, are set to their default values.
If I step the frequency down to 166MHz, my system is stable, but slower. Memtest and CPU-Z actually report it running at 157.2 MHz.
I've owned this motherboard for about 3 years now, and this issue only arose in recent history. Previously, I was able to use both sticks of ram in dual-channel mode at 200MHz.
My power supply is of a reputable brand (ASUS), and provides plenty of power (450W) for my setup.
I've tried playing around with the BIOS settings, but to no avail.