I recently acquired an old server with an Intel S5000VSA board, it currently has 8GB of RAM (8x 1GB sticks) and I added an extra two sticks although the DIMM slots I used are coming up as 'Memory disabled' in BIOS.
Is there a way I can enable these slots?
What is the part number of the memory modules you added? Have you tried to use these memory modules by themselves?
Usually, it is recommended using the larger memory in the blue slots first. Additionally, make sure you swap the memory around to make sure it is not an issue with the slots.