Cos I was bored , I looked again at the system
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1) all cables etc connected to correct wires / polarity correct / all cables new out of box
2) RAM / Graphics card inserted correctly
3) formatted and reinstalled Windows xp pro sp3 , slip-streamed disc with Nlite
disconnected 2 x 100mm additional case fans that I had connected to the mobo ( pwr_fan #5 in user manual and sys_fan #19 ) clicking much reduced , CPU fan operating much as normal , though overall temp up
CPU temp now showing 32c
So suspect Power supply cant provide enough power through motherboard
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If you have additional fans , try pulling the plug on them