Hi Mitchell - yeah, I'd another couple of runs on it last week - 3 before the system had even got booted up (i.e. nowhere near Win 7) again so beginning to think it's defo more a hardware issue now and thinking primarily of the PSU. If nothing else, it might prove the cheaper item to start replacing and so I'm hoping to do that shortly - but appreciate you checking the situation. Think we may just put this thread to bed for a bit now and see if I can resolve the hardware side of things first which will take me some weeks possibly as finances are beyond stretched just now. Given the intermittent nature of the problem it's hard to know how long to give it after I replace the PSU before I'd know it was sorted anyway, and now I'm pretty convinced it's not a Win 7 issue or software of any form, I'm content to close this help request . But thanks again - you've been great at working alongside me in getting to help me figure things out better.