Now,
I have installed the new hard drive, took a bit of time, but it all installed with no major dramas, except the occaisional crash during all of the detection cycles when windows has loaded and then proceeds to change and load drivers. The crashes were just immediate shut downs, then the machine would sometimes hang during the boot cycle or immediately switch off.
When using it last night (tentatively) the screen froze, and the system needed rebooting, it did this twice before I removed myself from the room. If I have time tonight I'll remove the other stick of memory (as per my post a couple of days ago, for some reason it never occurred to me that the original stick of memory could fail, blinded by frustration?) to see whether that is the problem, after that I only have my graphics card left before I can only blame the motherboard.
Thanks for all of your suggestions and help, if anyone has any other suggestions/guidance it will still be accepted gratefully.
Cheers,
J.