RAM problems

I have 2 computers, both Dell Optiplex 780 DT models.
I wanted to upgrade the RAM as there was only 2GB of DDR3 in each.
I bought sticks of Corsair XMS3 from ebay, mostly second-hand (used).
All but 1 stick was OK. That faulty stick gave Blue Screen of Death after 10 minutes or so.
I returned it to Corsair, hoping to avail of their lifetime warranty.

They have now sent me a new stick.
This stick, when installed singly or with the other sticks, gives a new fault.
Both pcs refuse to POST.
The fan starts without touching the power button, but the monitor stays black.

I seem to remember needing to reset the cmos battery, but haven't done that, thinking "what's the difference between the existing sticks and the new one"?

Each stick is 4GB, making 16GB in total. I've tried the new stick in each of the 4 dimm slots and get the same problem.

I suspect the new stick, but I'd expect it to have been tested before dispatch from the factory.
Could airport x-ray machines have damaged it?
No external signs of damage and it was very well packed.

Any help very welcome, please.

Thanks, I'll try that.
I know ebay is dicey but 16GB of XMS3 DDR3 RAM costs £130 on Amazon and I needed to upgrade 2 PCs.
£260 is a lot to spend.

What bothers me is that I've tried the new stick on each of the 2 PCs and in each of the DIMM slots.
I get the same result in all cases.
It seems to point to the new stick being faulty.
By the way, every stick is identical. They are all Corsair XMS3 DDR3 4GB apiece. The only difference is the "Version number" whatever that is.

I suppose I was a bit greedy.
I use my PCs quite a bit and download lots of bittorrent stuff.
If you have several files downloading at once it seems to use lots of memory resource.
Probably I didn't actually need 16GB each, but that is what I bought.

I'm just surprised that a brand new stick, sent all the way from Taiwan, would appear faulty on receipt.

Thank you.
The problem now is with a brand new stick, sent via UPS direct from Taiwan.
I was extremely impressed with their tracking data. It showed every step from Taiwan, to AbuDhabi, to India, to Germany, to Netherlands and over to the UK.
I was less than impressed with the stick when it arrived but it might just be the system cmos battery which is now 4 years old in both PCs.

Once the PC is switched on, is the system voltage maintained from the power supply?
I thought the cmos just maintained settings when the PC was off.

The answer seems a bit closer.
I emailed the technical team at Corsair in USA.
This is their reply:
Based on Intel's specification for their Q45 chipset, the memory controller can read up to 2Gb IC modules:

2Gb IC, single rank (8 IC chips total on module) = 2GB module
2Gb IC, dual rank (16 IC chips on module) = 4GB module
4Gb IC, single rank (8 IC) = 4GB module

As you can see, there are two ways to create a memory module - a dual rank, lower density IC or a single rank, high density IC. If the CMX4GX3M1A1333C9 does not work on your system, it is more than likely that it is based on the 4Gb IC technology which the Q45 chipset cannot use. I mentioned "likely" because the IC chip market is very dynamic and as such, our modules are manufactured based on the availability of these chips.

The problem is that they don't distinguish between 4GB modules that are low density or high density.
How daft is that?

I changed the cmos battery and drained residual current before putting the new CR2032 battery in. No good.
I think I have my answer now and will update this post when Corsair decide what they can do.

Thank you. Very helpful.
Corsair seem embarrassed as this is a known problem.
They use exactly the same item number (SKU) whether their modules contain high density or low density chips.
The former is OK for 10% of PCs and the latter for 100% of PCs.
I think that's significant.
They don't.