Install the new memory by itself and see if the system runs at 200MHz and see what the timings are. Sounds like you have a memory mismatch issue and the system is trying to run the memory at messed up timings. Try a BIOS update and re-install your video card drivers.
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When responding please provide your full system specs; hardware and software, OS, BIOS, drivers Etc. You can e-mailmemory related questions to firstname.lastname@example.org