Update:
Trying the Patriot Intel Extreme Masters RAM worked ok, so I tried eliminating the original sticks of RAM by doing a pair at a time. Then I found that if I put the sticks back to their original pair (I bought 2 pairs), the system boots ok now.
However, when I run the latest CPU-Z utility, it's memory tab is not populated with the memory timings, just the information at the top of the tab. The SPD tab shows the memory correctly.