Interesting - thank you for replying.
No issues with direct x or the memory, however looking in the reliability monitor revealed 3 critical crashes (at 4am I left the pc on with FC3 running) with the detail I mentioned above.
More interesting to me was there were about a hundred (every 15 mins or so) 'hardware errors' all relating to LiveKernelEvent, see details below:
Description **A problem with your hardware caused Windows to stop working correctly. Problem signature Problem Event Name: LiveKernelEvent Code: 3000040 Parameter 1: 2 Parameter 2: fffffc8c0f579620 Parameter 3: 1b0 Parameter 4: 0 OS version: 10018363 Service Pack: 0_0 Product: 768_1 OS Version: 10.0.18318.104.22.168.768.101 Locale ID: 2057**
Do you reckon this is related?