Thank you very much guys, for your suggestions.
I moved the RAM, tried one at the time with the same result. I couldn't used the old RAM cause i haven't it anymore.
Yes, there is power to the screen, for few sec i can see the start page of Window.
The pc seems quiet clean inside, more than mine anyway

i do think they cleaned it when they repaired it.
I checked all the connections i could, and they seemed connected properly.
I have another pc, it's one my daughter used (now she has a labtop), do you think it's possible to move my wife's hard disk to that pc, so that she can use it?
Sorry to bother you guys, but right now i can't afford another "visit" to the technician (last costed me 500$)

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Thanks again.
xxIENAxx