Well - upon further research - I've found that the problem lies in a fairly common issue with Nvidia drivers causing freezes. There doesn't appear to be a fix; I have to use the power-switch to manually reboot the PC when it locks up. I'm willing to tolerate the issue - it only occurs around once a day - but does manually cutting power to a windows installation, on a regular basis, damage any of my hardware? (I'm aware it may cause OS corruption).
Aware this is now probably in the wrong area but didn't want to make a new thread. Thanks for any help.