Help diagnosing strange RAM issue

[Mr. Peri Peri]

Hi,

My system is getting on a bit but I wanted to increase the RAM so bought some second hand, and having a very weird issue I’m struggling to diagnose.

Currently have 2 x 4GB modules - both RAM slots work.

I’ve bought 2 x 8GB modules.

Both modules work individually, but only in Slot 2.

If I put an 8GB module in Slot 1, the PC won’t boot (fans start up and then it resets, no video output, can’t even get in the BIOS).

It does work with a 4GB module in Slot 1, and an 8GB module in Slot 2.

I’ve run a memtest on both new modules with no errors, updated BIOS to latest version, reset BIOS defaults and also done a CMOS reset but no luck resolving the issue.

Components are:

Asus H81M-Plus mobo
Intel i5-4460
Corsair Vengeance Pro 16GB (2 x 8GB) 1600MHz

Has anyone got any ideas or suggestions?

It seems that the RAM is healthy, and so are the slots given that the old RAM works, the new RAM seems to be the correct spec - I’m at a loss as to why it’s not working.

Any help would be very much appreciated.

Thanks,

Phil