If you tried each chip independently it may be safe to assume the type is unsupported. You should however reset the CMOS and check the bios settings:
unplug PC, Remove Statis from hands by touching unpainted case metal, remove the CMOS (Silver button) battery for 30 minutes or so, replace battery, turn on, reset your bios values-save and exit.
The layout and wording of each BIOS is different, but it will be something like Reset or Default Values. Turn the computer off and on again, then keep tapping F8 before Windows starts to load until the BIOS appears. Make the change, save settings (important) and exit to reboot back into Windows.
You should look up the Voltage of your intended replacement ram so you know what to set the bios too.
Hope this helps!
