Check your original ram label. It's probably non-ecc. On page 82 of your dell manual, it specifically states that you can't mix ecc with non-ecc ram. Use your original ram label to find some cheap non-ecc ram. I sometimes find dell owners on craigslist selling their old ram. Dell boards are sometimes very ram specific, as their bios' don't have any adjustments for ram speed, timings, voltage, etc.