If iammykyl is still there , please accept my apologies for not replying sooner, circumstances beyond my control, , and my sincere thanks for your help and advice.
New PSU as you recommended arrived and was subsequently fitted, by me, no big thing but, iv not dared to enter the world of the PC innards before, and DELL do not make it easy the wiring loom was immense, and ran everywhere there was no need to go.
After swap, PC booted without, a problem, seems a lot quicker than it used to be, but again iv taken off everything except, the OS, which iv upgraded to windows 10 and its running very well on this elderly PC.
So again, many thanks, for the advice and guidance , and the confidence to be able, albeit with a great deal of caution, to look at how I can improve this PC, perhaps with better DVD/Blue ray read and write.
Very best regards
P.S. i think that we can call this one closed very satisfactorily.