|My logic for deciding my problem was in the monitor itself and not the computer was based on mr Hill's advice.|
Although the monitor at switch on did not light, it blinks every time it's on off switch is pushed.
The computer at switch on does goes through the XP start up routine.
So toggling on off the monitor you can see briefly each stage of the start up sequence meaning the computer is up and running.
Having said that, the monitor I found would light normally with about half an hour's warming up switched on.
So with this pre-heating and then switching on the computer, the monitor stays on correctly for a whole day if needed, and you can use the computer normally.
I bought another monitor because
1. The service people couldn't diagnose directly the fault( maybe something in the power supply...) they said.
2. the repair price is about 75% of a new monitor, not including parts.
So as for fault finding on what is today basically a consumer article..... don't waste your time.