Seemingly random shutdowns

Hello everyone :)

I've just installed a fresh copy of windows 7 onto my ssd, all updates are installed and up to date.
My screen will go blank (no signal) and it sounds like its doing a power cycle (the fans speed up a little) then it just hangs at a blank screen. This happens randomy 3 or 4 times in a row or not at all for days. It seems to only happen if I'm browsing the web or if the system is idle. Not witnessed it happening whilst the system is being stressed. I've ran all the usual stress tests and they all passed with acceptable temperatures. I ran Memtest overnight and managed 10 passes but turning system off. Blue Screen View software isn't showing any dump files to analyse yet the dm log collector showed 1 dmp file which was access denied (tried running as admin to no effect) I've exhaused my limited knowledge and am at a loss.

Hope you can help

Not 100% sure but I may of fixed it. My daughter comes running in the room and jumps and the thump on the floor coincided with a crash. So I opened my rig up and rebedded everything. Just jumped again and no crash.. Now it maybe a total coincidence so I'm not holding my breath :)