System Refuses To Boot After Memory Upgrade

I've just tried to upgrade my PC's memory from 8GB to 16GB and have hit a rather worrying problem in that the PC now refuses to boot. Initially, once I'd replaced the old memory modules with the new ones, I got three beeps on power-up, which I quickly established was the result of my not properly seating the modules. Once I'd made sure they were firmly inserted I tried again, and this time all I get is the computer powering up - so all the lights come on and the fans kick into life - but then it powers down again without even attempting to boot: I don't even get to the BIOS. After a few tries I decided that it might be an issue with one or more of the new modules, so I swapped them back to the original 8GB kit and I still get the same problem. My PC is essentially DOA. Whilst I was inserting/re-inserting modules I did try to avoid and issues with static discharge. I wonder if perhaps I've disturbed a connector somewhere, although I couldn't see any signs of this when I re-opened the case to check.

The new modules are a 16GB Corsair Vengence DDR3 dual-channel 4-module kit (4x4GB). They were replacing a 4 module 8GB DDR3 dual-channel kit (4x2GB), so in both cases all four slots were in use. Motherboard is an Intel DP55WG, which is listed by Corsair as being compatable (16GB is the max for this motherboard). I've been running this system for two years prior to my upgrade attempt this evening, and it's been rock solid with no issues.

Maybe I should reset the CMOS for instance? Note that I'm not a hardware guy, and messing around inside the case isn't something I normally even consider trying... But I thought that this would be a very simple, trouble-free upgrade!