Good , glad that things are moving forward quite well  [URL] Check this manual, page 51 has the supported memory configurations. Now, about finding the faulty ram... one way would be to remove one good module, and use that slot to test the rest of the ram one by one (assuming that the moment you put a faulty inside, the system would be again not working as before).
Hi I had a motherboard replaced by dell after it blew about 6-7 months ago.  It was running fine for a few months and then just as the parts warranty ran out it suddenly it failed to boot. After dell told me that they were unable to help as the part was out of warranty and stock. I left the PC in the corner for about a month or two. I then randomly tried to power it on and it suddenly worked. Everything was fine it booted up a couple of times and I assumed the problem had somehow fixed itself. About a week later it's suddenly failing to boot again. The symptoms are as follows:     If anyone has any information on how to solve any of this I would be truly grateful, A 
Dell Precision Tower 7910 Power light comes on but fails to boot BIOS