Thanks for the reply, and sorry for the delay in getting back to you,
No is the easy answer, I'm a nontechnical, the most iv ever done is replace the PSU, when I say a clean install what I actually mean is that the HD on the system is only used for software all info is kept on a number of external drives or my NAS.
So since purchase the OS has gradually been upgraded form vista, through Xp, to w7, W8, and recently to W10.
At the same time as replacing the PSU I checked for a bios update and reflashed to A07, and then an install of office2016.
Since then all has been great, the system is used mainly for report writing and photographs.
I had wondered if the HDs, had gone down but don't know how to check, or if it's worth trying th dell boot disk, as the system does not seem able to find any drives to boot from, but when I run the diagnostic everything is coming back as passed.